Efficient peptide coupling involving sterically hindered amino acids

Hindered amino acids have been introduced into peptide chains by coupling N-(Cbz- and Fmoc-alpha-aminoacyl)benzotriazoles with amino acids, wherein at least one of the components was sterically hindered, to provide compounds 3a-e, (3c +3 c'), 5a-d, (5a + 5a'), 6a-c, (6b + 6b'), 8a-c, 9a-e, 10a-d, and (10a + 10a') in isolated yields of 41-95% with complete retention of chirality as evidenced by NMR and HPLC analysis. The benzotriazole activation methodology is a new route for the synthesis of sterically hindered peptides. (Note: compound numbers written within brackets represent diastereomeric mixtures or racemates; compound numbers without brackets represent enantiomers.).     

Solid phase synthesis and application of trisubstituted thioureas

Resin-bound amines 1a-e condense with isothiocyanates to give thiourea resins 2a-i. Resins 2a-g subsequently react with iodomethane followed by cleavage affording S-methyl isothioureas 4a-g, and resins 2a-b,h-i react with acyl chlorides to afford N-acylated thioureas 6a-d. N-Acylthioureas 8a-f (R(2) = H) were prepared directly from resin-bound amines 1a-d with acyl isothiocyanates. N-Acylthioureas 8a-d,f(R(2) = H) were used for the preparation of S-methyl-N-acylisothioureas 10a-e. Alkylation was performed using methyl iodide. Resin-bound S-methyl-N-acylisothioureas 10a,b,d are converted by an action of hydrazines into 3-amino-1,2,4-triazoles 13a-d. Condensation of resins 8a-e (R(2) = H) with 2-bromoacetophenones in the presence of TEA affords thiazoles 15 a-e. All transformations proceeded in high yields and gave products of good purities.     

Photolysis of acetyl esters of 2,2′-dinitrodiphenyl-carbinols in protic and aprotic solvents

Irradiation ofacetyl esters of 2,2′-dinitrodiphenyl-carbinols (1a-d) in aprotic medium like 2-propanol yielded dibenzol [c,f]-[1,2]diazepin-11-one-5-oxides (5a-d) as the major product. Dibenzoi[c,f]-[1,2]diazepin-11-one (2a-d), 2,2′-dinitrobenzophenones (3a-d), 2-amino-2′-nitrobenzophenones (4a-d), and N-hydroxyacridones (6a-d) were also formed in varying amounts. Irradiation of 1a-d in an aprotic medium like benzene yielded the above products along with benzisoxazoles (7a-d) also. When triethylamine was used as the solvent the major product obtained was N-hydroxyacridones (6a-d). Plausible mechanisms for the formation of the products are discussed     

Rearrangement reactions of heterocycles. 12. Rearrangement of 6-substituted pyrido[1,2-a]pyrimidines to isomeric 1,8-naphthyridines and some of their further reactions

2-Amino-6-methylpyridine ( 4 ) reacts with active malonates 2a-d or 3a-d either in acetone solution with triethylamine as catalyst at room temperature or with active malonates 2a-d in acetone solution at reflux temperature to yield the pyrido[1,2-a]pyrimidines 5a-d . 2,6-Diaminopyridine ( 8 ) already reacts without triethylamine with 2a-d at room temperature to afford the pyrido[1,2-a]pyrimidines 9a-d . At higher temperatures pyrido[1,2-a]pyrimidines 5 and 9 are rearranged via ketene intermediates [1] to yield the 1,8-naphthyridines 6a-d , and 10a-d , respectively. The naphthyridines 6 and 10 can also be synthesized directly from 4 or 8 using either diethyl malonates 1 or — with better results — the active malonates 2 at 240–250°. Further reaction of 10a-e with 2c,d leads to the pyridonaphthyridines 12a-f . Nitration of 6c yields the nitro derivative 16 and chlorination of 6c,d gives 15c,d , while the chlorination of 10c affords the di-chloro derivative 17 .     

Functionalized chiral vinyl aminosulfoxonium salts: asymmetric synthesis and application to the synthesis of enantiopure unsaturated prolines, beta,gamma-dehydro amino acids, and cyclopentanoid keto aminosulfoxonium ylides

Methylation of the enantiopure functionalized vinyl sulfoximines 5a-e and 14a-d followed by a F- ion or DBU-mediated isomerization of the vinyl aminosulfoxonium salts 7a-e and 15a-d, respectively, gave the allyl aminosulfoxonium salts 10a-e and 17a-d, respectively. A concomitant intramolecular substitution of the aminosulfoxonium group of 10a-e and 17a-d by the amino group afforded the unsaturated prolines 8a-e and 18a-d, respectively. The starting vinyl sulfoximines are accessible through a highly selective and stereo-complementary aminoalkylation of the corresponding sulfonimidoyl-substituted mono- and bis(allyl)titanium complexes with the imino ester 4. The vinyl aminosulfoxonium salts 34, 7a-d, and E-15c experienced upon treatment with the Cl- ion a migratory substitution with formation of the delta-chloro-beta,gamma-dehydro amino acids 36, E/Z-37a-d, and 38, respectively. A migratory substitution of the hydroxy-substituted vinyl aminosulfoxonium salts 46a and 46b furnished the delta-chloro allyl alcohols E/Z-48a and E-48b, respectively. A facile one-pot conversion of the vinyl sulfoximines 31b, 5c and 45a to the allyl chlorides 36, E/Z-37c and E/Z-48a, respectively, was achieved upon treatment with a chloroformiate. A tandem cyclization of the vinyl aminosulfoxonium salts 7b, Al-7b and 57 with LiN(H)tBu yielded the cyclopentanoid keto aminosulfoxonium ylides 54, Al-54, 59, 60 and 61, respectively. The structure of the tricyclic keto aminosulfoxonium ylide Al-54 has been determined by X-ray crystal structure analysis. Ab initio calculations and a NBO analysis of the tricyclic keto aminosulfoxonium ylide XXIII show a polar structure stabilized by electrostatic interactions between the ylidic C atom and both the carbonyl C atom and the S atom.     

Formation and chemical reactivities of a new type of double-butterfly [[Fe2(mu-CO)(CO)6]2(mu-SZS-mu)]2-: synthetic and structural studies on novel linear and macrocyclic butterfly Fe/E (E=S,Se) cluster complexes

A new type of double-butterfly [[Fe(2)(mu-CO)(CO)(6)](2)(mu-SZS-mu)](2-) (3), a dianion that has two mu-CO ligands, has been synthesized from dithiol HSZSH (Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)), [Fe(3)(CO)(12)], and Et(3)N in a molar ratio of 1:2:2 at room temperature. Interestingly, the in situ reactions of dianions 3 with various electrophiles affords a series of novel linear and macrocyclic butterfly Fe/E (E=S, Se) cluster complexes. For instance, while reactions of 3 with PhC(O)Cl and Ph(2)PCl give linear clusters [[Fe(2)(mu-PhCO)(CO)(6)](2)(mu-SZS-mu)] (4 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)) and [[Fe(2)(mu-Ph(2)P)(CO)(6)](2)(mu-SZS-mu)] (5 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)), reactions with CS(2) followed by treatment with monohalides RX or dihalides X-Y-X give both linear clusters [[Fe(2)(mu-RCS(2))(CO)(6)](2)(mu-SZS-mu)] (6 a-e: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2), FeCp(CO)(2)) and macrocyclic clusters [[Fe(2)(CO)(6)](2)(mu-SZS-mu)(mu-CS(2)YCS(2)-mu)] (7 a-e: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2); Y=(CH(2))(2-4), 1,3,5-Me(CH(2))(2)C(6)H(3), 1,4-(CH(2))(2)C(6)H(4)). In addition, reactions of dianions 3 with [Fe(2)(mu-S(2))(CO)(6)] followed by treatment with RX or X-Y-X give linear clusters [[[Fe(2)(CO)(6)](2)(mu-RS)(mu(4)-S)](2)(mu-SZS-mu)] (8 a-c: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2)) and macrocyclic clusters [[[Fe(2)(CO)(6)](2)(mu(4)-S)](2)(mu-SYS-mu)(mu-SZS-mu)] (9 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2); Y=(CH(2))(4)), and reactions with SeCl(2) afford macrocycles [[Fe(2)(CO)(6)](2)(mu(4)-Se)(mu-SZS-mu)] (10 d: Z=CH(2)(CH(2)OCH(2))(3)CH(2)) and [[[Fe(2)(CO)(6)](2)(mu(4)-Se)](2)(mu-SZS-mu)(2)] (11 a-d: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)). Production pathways have been suggested; these involve initial nucleophilic attacks by the Fe-centered dianions 3 at the corresponding electrophiles. All the products are new and have been characterized by combustion analysis and spectroscopy, and by X-ray diffraction techniques for 6 c, 7 d, 9 b, 10 d, and 11 c in particular. X-ray diffraction analyses revealed that the double-butterfly cluster core Fe(4)S(2)Se in 10 d is severely distorted in comparison to that in 11 c. In view of the Z chains in 10 a-c being shorter than the chain in 10 d, the double cluster core Fe(4)S(2)Se in 10 a-c would be expected to be even more severely distorted, a possible reason for why 10 a-c could not be formed.     

Synthesis of C60-fused tetrahydrothiophene derivatives via nucleophilic cycloaddition of thiocyanates

Nucleophilic cycloaddition of thiocyanates 1a-e with C60 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene afforded C60-fused 2-iminotetrahydrothiophene derivatives 2a-e and methanofullerenes 3a-d. The product distributions were highly sensitive to the substrates employed. The 2-iminotetrahydrothiophene derivatives 2a-e could be further manipulated by hydrolysis and acetylation to give 2-oxotetrahydrothiophene derivatives 4a-e and 2-acetamidotetrahydrothiophene derivatives 5a-e. A possible reaction mechanism for the formation of products 2a-e and 3a-d was proposed.     

A Convenient Preparation of 2-(2-Arylidene)- and 2-(2-Polyhydroxyalkylidene)hydrazono-4-imidazolidinones with Various Heterocyclic Side Chain Substituents at Position 5 as Potential Antiviral and Antitumor Agents

A variety of novel 5-[( Z )-arylidene]-2-[(2-( E )-arylidene)hydrazono]-4-imidazolidinones 1a-c to 4a , b and 5-[( Z )-arylidene]-2-[(2-( E )-polyhydroxyalkylidene)hydrazono]-4-imidazolidinones 5a-c to 7a-c were prepared from the reaction of 5-[( Z )-arylidene]-2-methylmercaptohydantoins 8a-c with 2-( E )-arylidene hydrazones 13a-d and/or 2-( E )-monosaccharides hydrazones 16a-c . The linear structure, and not that of the angular isomer, has been selected for the products. This structure has been confirmed from a model study of the condensation of 5-[( Z )-2-thienylidene]-2-hydrazono-4-imidazolidinone 9a with benzaldehyde and D -galactose, respectively. The acetylation and benzoylation reactions of compounds 1-7 have been studied. All the new compounds were tested for their potential antiviral and antitumor activities.     

Supramolecular photochirogenesis. 2. Enantiodifferentiating photoisomerization of cyclooctene included and sensitized by 6-O-modified cyclodextrins

Supramolecular enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to the chiral (E)-isomer (1E) via inclusion and sensitization by modified alpha-, beta-, and/or gamma-cyclodextrin derivatives, possessing benzoate (2a, 3a, 4a), isomeric phthalates (3b-d), and tethered benzamide (3e) chromophores, has been investigated in aqueous methanol solutions at varying temperatures. The photostationary-state 1E/1Z ratios obtained upon sensitization with 2-4 in 1:1 water-methanol reached 0.4-0.8, which are higher than the value of ca. 0.25 reported for sensitizations by conventional alkyl benzoates in hydrocarbon solvents, although the ratio was reduced to 0.2-0.4 in water or methanol. The sensitizations of 1Z by alpha- and gamma-cyclodextrin benzoates (2a, 4a) with size-mismatched cavities gave 1E of poor enantiomeric excesses (ee's) smaller than 3 and 5%, respectively. In contrast, beta-cyclodextrin derivatives (3a-e) afforded much higher ee's of up to 24%, depending on the solvent composition. Thus, the modification of cyclodextrin with a sensitizing group successfully enhanced the product through the excited-state supramolecular interaction within the cavity. Interestingly, the product ee's obtained with benzoate 3a and methyl phthalate 3b are not a simple function of either temperature or solvent, but are nicely correlated with the host occupancy or the percentage of occupied host. This means that the entropy factor plays an insignificant role in this supramolecular photochirogenesis system, which is in sharp contrast to the decisive role of entropy in the conventional (nonsupramolecular) counterpart performed in homogeneous solutions, where an inversion of product chirality by temperature variation is reported to occur.     

Highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides from 1-bromo-1-fluoroalkenes via palladium-catalyzed carbonylation reactions

The highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), which are readily available starting materials, have been found to isomerize to high E/Z ratios after storage at -20 degrees C for 1 week or by photolysis at 254 nm. Since the (E)-isomers have been found to react faster than the corresponding (Z)-isomers at room temperature in Pd(0)-catalyzed reactions, the palladium-catalyzed carboalkoxylation of high E/Z 1-bromo-1-fluoroalkenes lead to a high Z/E (Z/E >/= 98:2) ratio of the alpha-fluoro-alpha,beta-unsaturated esters. When 1-bromo-1-fluoroalkenes (E/Z approximately 1:1) were reacted with HCOOH/NBu(3)/Pd(II)/DMF, the (E)-isomer was selectively reduced, and the remaining (Z)-1-bromo-1-fluoroalkenes were recovered in essentially pure isomeric form. The resulting mixture of (Z)-1-bromo-1-fluoroalkenes and the reduced products underwent similar palladium-catalyzed carboalkoxylation reactions at 70 degrees C, and the (E)-alpha-fluoro-alpha,beta-unsaturated esters were stereospecifically obtained. This methodology was also successfully applied for the stereospecific synthesis of (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides: the palladium-catalyzed carboamidation reaction of high E/Z and (Z)-1-bromo-1-fluoroalkenes lead to pure (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides, respectively.     

Peri- and enantioselectivity of thermal, scandium-, and [pybox/scandium]-catalyzed Diels-Alder and hetero-Diels-Alder reactions of methyl (E)-2-oxo-4-aryl-butenoates with cyclopentadiene

The cycloaddition between methyl (E)-2-oxo-4-aryl-3-butenoates (2 a-d) and cyclopentadiene, in addition to the expected normal Diels-Alder (DA) adducts endo-3 a-d and exo-4 a-d, gives the less expected endo-5 a-d products of the [4+2] hetero-Diels-Alder (HDA) reaction in which the alpha-ketoester behaves as a heterodiene. If a comparison is made between the thermal and the scandium(III) triflate-catalyzed conditions, the periselectivity changes and whereas under thermal conditions the main products are those from the DA reaction (3 a-d), in the presence of Sc(OTf)3 (OTf=triflate), the HDA products 5 a-d become largely predominant. The reactions are enantioselectively catalyzed by the scandium(III) triflate complex of (4'S,5'S)-2,6-bis[4'-(triisopropylsilyl)oxymethyl-5'-phenyl-1',3'-oxazolin-2'-yl]pyridine (1) and both the DA and the HDA products are obtained with excellent enantiomeric excess, up to >99% ee. The X-ray crystallographic structure determination of 5 c assigns it the 4R,4aS,7aR absolute configuration. The thermal retro-Claisen rearrangement of 3 c into (4R,4aS,7aR)-5 c allows the correlation of their absolute configuration, and 3 c has therefore the 2R,3R configuration. By analogy the same absolute configuration can be assigned to 3 a,b,d and 5 a,b,d, and the stereospecific thermal Claisen rearrangement of the optically active 5 a,b,d into 3 a,b,d completes the correlation between their absolute configuration. The [3,3]-sigmatropic rearrangements can be easily carried out under catalytic conditions with scandium(III) triflate, which promotes the equilibration between 3 a-d and 5 a-d, with a different degree of enantioselectivity characterizing the process starting from 3 a-d or 5 a-d. The unambiguous attributions of the configuration to the products allows us to propose a rationale of the stereochemical outcome of the catalyzed cycloaddition and to investigate the reaction mechanism of the competing DA and HDA reactions and shifts in products distribution by acid catalysis.     

Photochemistry of bicyclo[2.2.2]oct-7-ene-2,5-diones and the corresponding 5-hydroxyimino and 5-methylene derivatives

Synthesis and photochemistry of several title compounds 1-3 containing multiple chromophoric systems are described. The Diels-Alder reactions of 2,6,6-trimethylcyclohexa-2,4-dienone (5) with acetylenes 6a-d provided the adducts 7a-d, which upon hydrolysis furnished the desired bicyclo[2.2.2]octenediones 1a-d. Oximes 2a-d were prepared from diones 1a-d by treatment with hydroxylamine hydrochloride in pyridine. 5-Methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d were obtained via chemoselective Wittig reaction of the corresponding diones 1a-d. Bicyclo[2.2.2]octenediones 1a-c underwent chemoselective oxa-di-pi-methane rearrangement under sensitized conditions and suffered formal ketene extrusion upon direct irradiation. Direct irradiation of 1d afforded 11d via formal ketene extrusion but under sensitization it remained unchanged. Oximes 2a-d suffered ketene extrusion upon direct irradiation and E/Z isomerization under sensitized conditions. On the other hand, 5-methylenebicyclo[2.2.2]oct-7-en-2-ones 3a-d generally underwent 1,3-acyl shift. The plausible courses of all these photochemical processes are discussed.     

Synthesis of some new 4,5-substituted-4H-1,2,4-triazole-3-thiol derivatives

In this study appropriate hydrazide compounds, furan-2-carboxylic acid hydrazide (1) and phenylacetic acid hydrazide (2) were converted into 1,4-substituted thiosemicarbazides 4a-e and 5a-e and 4-amino-5-(furan-2-yl or benzyl)-4H-1,2,4-triazole-3-thiols 7 and 10. The 1,4-substituted thiosemicarbazides were then converted into 5-(furan-2-yl or benzyl)-4-(aryl)-4H-1,2,4-triazole-3-thiols 8a-e and 9a-e. In addition, the azomethines 11a-d and 12a-d were prepared from the corresponding arylaldehydes and the 4-amino-5-(furan-2-yl or benzyl)-4H-1,2,4-triazole-3-thiols 7 and 10. The structures of all the synthesized compounds were confirmed by elemental analyses, IR, (1)H-NMR and(13) C-NMR spectra.     

Synthesis of polyhydroxylated 2H-azirines and 2-halo-2H-azirines from 3-azido-2,3-dideoxyhexopyranoses by alkoxyl radical fragmentation

The reaction of 3-azido-2,3-dideoxypyranose and 3-azido-2,3-dideoxy-2-halohexopyranose compounds with (diacetoxyiodo)benzene and iodine generated 2-azido-1,2-dideoxy-1-iodoalditols and 2-azido-1,2-dideoxy-1-halo-1-iodoalditols, respectively. These beta-iodo azides could be transformed by chemoselective dehydroiodination into 2-azido-1,2-dideoxy-4- O-formyl-pent-1-enitols and (Z, E)-2-azido-1,2-dideoxy-1-halo-4- O-formyl-pent-1-enitols in good yields. Thermolysis and photochemical studies of these vinyl azides and 1-halovinyl azides for the synthesis of polyhydroxylated 3-alkyl-2 H-azirines and the hitherto unknown 2-halo-3-alkyl-2 H-azirines have also been accomplished.     

Stereocontrolled synthesis of 6-s-cis- and 6-s-trans-locked 9Z-retinoids by hydroxyl-accelerated Stille coupling of (Z)-tri-n-butylstannylbut-2-en-1-ol and bicyclic dienyl triflates

Analogues of 9-cis-retinoic acid with locked 6-s-cis and 6-s-trans conformations have been stereoselectively synthesized using a Stille coupling reaction between bicyclic dienyl triflates (5and 6, respectively) and (Z)-tributylstannylbut-2-en-1-ol (7) to stablish the Z geometry of the polyenic side chain. The mild conditions (25 degrees C, 30 min) of this coupling stand in contrast to the reluctance of the isomeric (E)-tributylstannylbut-2-en-1-ol (18) to react with triflates 5/6. The significant rate differences experimentally observed in Stille reactions between isomeric (Z)- and (E)-tri-n-butylstannylalkenols in favor of the former isomer, even with highly hindered alkenyl triflates, is ascribed to internal coordination of palladium to the heteroatom in the presumably rate-limiting transmetalation step. Dienals and trienals with an E geometry, which are not efficiently available by direct coupling of the corresponding triflates and E-stannanes, can in turn be obtained by isomerization of their Z-isomers.     

Highly selective addition of chiral,sulfonimidoyl substituted bis(allyl)titanium complexes to N-sulfonyl alpha-imino esters: asymmetric synthesis of gamma,delta-unsaturated alpha-amino acids bearing a chiral,electron-withdrawing nucleofuge at the delta-position

Selective addition of the chiral, sulfonimidoyl substituted bis(allyl)titanium complexes 5a-d, which are configurationally labile in regard to the Calpha-atoms, to N-toluenesulfonyl (Ts)-, N-2-trimethylsilylethanesulfonyl (SES)-, and N-tert-butylsulfonyl (Bus) alpha-imino ester (9a-c) in the presence of Ti(OiPr)(4) and ClTi(OiPr)(3) afforded with high regio- and diastereoselectivities in good yields the (syn, E)-configured beta-alkyl-gamma,delta-unsaturated alpha-amino acid derivatives 2a-g, which carry a chiral, electron-withdrawing nucleofuge at the delta-position and a cyclohexyl, an isopropyl, a phenyl, and a methyl group at the beta-position. Addition of the cyclic bis(allyl)titanium complex 14 to N-Bus alpha-imino ester 9c afforded with similar high regio- and diastereoselectivities the (E)- and (Z)-configured amino acid derivatives (E)-8 and (Z)-8. Reaction of complexes 5a-d with alpha-imino esters 9a-c in the presence of Ti(OiPr)(4) occurs stepwise to give first the mono(allyl)titanium complexes containing 2a-g as ligands, which react in the presence of ClTi(OiPr)(3) with a second molecule of 9a-c with formation of two molecules of 2a-g. Formation of (S,R,E)-configured homoallylic amines 2a-g entails Si,Re,E processes of alpha-imino esters 9a-c with the (R,R)-configured bis(allyl)titanium complexes (R,R)-5a-d and (R)-configured mono(allyl)titanium complexes (R)-17a-d, both of which are most likely in rapid equilibrium with their (S,S)-diastereomers and (S)-diastereomers, respectively. Interestingly, in the reaction of 5a-d with aldehydes, the (S,S)-configured complexes (S,S)-5a-d are the ones which react faster. Reaction of the N-titanated amino acid derivatives Ti-2a and Ti-2b with N-Ts alpha-imino ester 9a led to the highly diastereoselective formation of imidazolidinones 15a and 15b, respectively. Cleavage of the sulfonamide group of the N-Bus amino acid derivative 2d with CF(3)SO(3)H gave quantitatively the sulfonimidoyl functionalized amino acid H-2d. A Ni-catalyzed cross-coupling reaction of the amino acid derivative 2e with ZnPh(2) led to a substitution of the sulfonimidoyl group by a phenyl group and furnished the enantiomerically pure protected alpha-amino acid Bus-1. Two new N-sulfonyl alpha-imino esters, the SES and the Bus alpha-imino esters 9b and 9c, respectively, have been synthesized from the corresponding sulfonamides by the Kresze method in medium to good yields. The N-SES alpha-imino ester 9b and the N-Bus alpha-imino ester 9c should find many synthetic applications, in particular, in cases where the N-Ts alpha-imino ester 9a had been used before.     

Hydrozirconation of stannylacetylenes. Synthesis and reactions of ketene Stannyl(Telluro) acetals

Stannylacetylenes 7a-e react with Cp(2)Zr(H)Cl in THF at room temperature to give the alpha-zirconated vinylstannane intermediates 8a-e, which subsequently react with butyltellurenyl bromide (2.0 equiv) to give exclusively ketene stannyl(telluro) acetals 6a-e of E configuration. Similar reactions were performed using phenylselenenyl bromide (2.0 equiv) as the electrophile, but a mixture of products was formed including the expected ketene stannyl(seleno) acetals 12. Otherwise, the use of 1.4 equiv of Cp(2)Zr(H)Cl and 1.0 equiv of PhSeBr results in the exclusive formation of 12, in good yields. Treatment of ketene stannyl(telluro) acetals with iodine or NBS followed by reductive dehalogenation results in the formation of 1-iodo-1-telluroalkenes 4a-e and 1-bromo-1-telluroalkenes 5a-e, respectively, with total retention of the configuration.     

Nucleophilic di- and tetrafluorination of dicarbonyl compounds

Reactions of various diketo compounds with Deoxofluor [(CH(3)OCH(2)CH(2))(2)NSF(3)] have been investigated. When reacted with Deoxofluor, alpha-diketones, R(1)COCOR(2) (R(1) = R(2) = Ph; R(1) = R(2) = 4-Me-C(6)H(4); R(1) = Ph, R(2) = Me; R(1) = Me, R(2) = Et) (1a-d) formed difluoro derivatives (2a-d) in the presence of a catalytic amount of HF and/or tetrafluoro (3a-d) products depending on the reaction conditions and stoichiometry used. Reactions of beta-diketones, R(3)COCH(2)COR(4) (R(3) = R(4) = Ph; R(3) = R(4) = Me; R(3) = Me, R(4) = Ph) (4e-g), with Deoxofluor in the presence of a catalytic amount of HF led to the formation of difluoroalkenones as a mixture of E (5e-g) and Z (6e-g) isomers in good yield. Reaction of other diones, R(5)CO-X-COR(6) (R(5) = R(6) = Ph, X = -CH=CH-; R(5) = R(6) = Me, X = -C(6)H(4)C(6)H(4)-; R(5) = R(6) = Ph, X = -CH(2)CH(2)CH(2)-; R(5) = R(6) = Me, X = -CH(2)CH(2)-) (7h-k) with Deoxofluor produced mainly difluoro products (8h-k) with low yields of tertrafluoro derivatives (9h-k). Acyclic alpha-keto amides react poorly to give the corresponding difluoro derivatives, whereas cyclic alpha-keto amides (10l-p) react smoothly under very mild conditions to produce the corresponding difluoro products (11l-p) in >88% isolated yield.     

Studies on Organophosphorus Compounds: Synthesis and Reactions of Some New 5′-Cyano-2′-(4-methoxyphenyl)spiro[cycloalkane-1,6′-[1,3,2]thiazaphosphixane]-2′,4′-disulfide Derivatives

2,4-Bis(4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's Reagent, LR, 1 ) reacts with cycloalkylidenecyanothioacetamides ( 2 and 3 ) to give 5'-cyano-2'-(4-methoxyphenyl)spiro [cyclopentane(cyclohexane)-1,6'-perhydro-[1,3,2]thiazaphosphixane]-2',4'-disulfide ( 4 and 5 ). The reaction of compounds 4 and 5 with f -halo compounds led to the formation of the substituted thio-compounds 6a-e and 7a-e , respectively, these compounds, upon treatment with sodium ethoxide, produce the corresponding thienothiazaphosphixine derivatives 8a-e and 9a-e respectively. Compounds 8a-e and 9a-e react with LR under different reaction conditions to give polyfused heterocyclic compounds 10a-d and 11a-d respectively. Treatment of compounds 8b and 9b with CS 2 and (CH 3 ) 2 SO 4 gave the corresponding dithiocarbamate methyl ester derivatives 12 and 13 , respectively, which on treating with hydrazine hydrate yielded compounds 14 and 15 respectively. Compounds 14 and 15 reacted with LR to yield compounds 16a , b and 17a , b respectively.     

A new route to the improved synthesis of 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils

A new route to C-6-selenenyl analogs of compound 1a from 5-alkyl-6-chlorouracils 6a-b has been described. A mild and highly efficient synthesis of 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils 8a-e has been accomplished from 6a-b in good yields using a two step procedure. Silylation of 5-alkyl-6-chlorouracils 6a-b using N,O-bis(trimethylsilyl)acetamide followed by regioselective alkylation of the silylated intermediate with ethyl or benzyl chloromethyl ether in dichloromethane afforded the desired 1-(alkoxymethyl)-5-alkyl-6-chlorouracils 7a-d in 88–94% yields. Compounds 7a-d readily underwent addition-elimination reaction with an appropriate arylselenol in the presence of ethanolic sodium hyroxide to produce the corresponding 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils 8a-e in excellent yields (94–99%).