1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane and trimethylphosphite: unusual 1,4-dioxan-2,5-dione ring formation

1,1,3,3,3-Pentafluoro-2-pentafluorophenyl-1,2-epoxypropane 1 reacted with trimethylphosphite giving two diastereomers, (Z)- and (E)-3,6-bis(trifluoromethyl)-3,6-bis(pentafluorophenyl)-1,4-dioxan-2,5-dione 2a, b in a 1:1 ratio, cyclodimerisation product of the intermediately generated α-lactone 4. Compounds 2a, b were hydrolysed to furnish 3,3,3-trifluoro-2-hydroxy-2-(2,3,4,5,6-pentafluorophenyl)propionic acid 5.     

Reactions of guaiazulene with thiophene-2,5-dicarbaldehyde and furan-2,5-dicarbaldehyde in methanol in the presence of hexafluorophosphoric acid: a facile preparation and properties of delocalized dicarbenium-ion compounds stabilized by two 3-guaiazulenyl groups and a thiophene (or furan) ring

Reaction of guaiazulene (1) with thiophene-2,5-dicarbaldehyde (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 3 h gives as high as 90% isolated yield of the delocalized dicarbenium-ion compound, 2,5-thienylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (3). Similarly, reaction of 1 with furan-2,5-dicarbaldehyde (4) under the same conditions as the above reaction affords the corresponding dicarbenium-ion compound, 2,5-furylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (5), in 84% isolated yield. Along with a facile preparation and the spectroscopic and electrochemical properties of 3 and 5, comparative studies on the ¹H and ¹³C NMR spectral and chemical properties of 3 and 5 with those of the delocalized mono- and dicarbenium-ion compounds [i.e., (3-guaiazulenyl)(2-thienyl)methylium hexafluorophosphate (7), (2-furyl)(3-guaiazulenyl)methylium hexafluorophosphate (9), α,α′-bis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (10), 1,2-phenylenebis(3-guaiazulenylmethylium) bis(hexafluorophosphate) (11), and 1,4-phenylenebis(3-guaiazulenylmethylium) bis(tetrafluoroborate) (12)] are reported. Moreover, referring to the results of the X-ray crystallographic analyses of 7, 9, 11, and 12, the optimized 2,5-thienylenebis(3-guaiazulenylmethylium)- and 2,5-furylenebis(3-guaiazulenylmethylium)-ion structures for 3 and 5, calculated by a WinMOPAC (version 3.0) program using PM3 as a semiempirical Hamiltonian, are described.     

A convenient synthesis of new pyrido[3,2-e][1,4]diazepine-2,5-diones and pyrido[2,3-e][1,4]diazepine-2,5-diones

A convenient synthesis of a series of pyrido[3,2-e][1,4]-diazepine-2,5-diones 8 and pyrido[2,3-e][1,4]diazepine-2,5-diones 9, is reported using the condensation of α-amino acid methyl ester derivatives with 1H-pyrido[3,2-d][1,3]oxazine-2,4-dione and 1H-pyrido[2,3-d][1,3]oxazine-2,4-dione. Compounds 8 and 9 were also synthesized by peptide coupling of α-amino acid methyl ester derivatives with β-amino acids (2 or 3) followed by the cyclisation in tetrahydrofuran with sodium hydride (NaH).     

A facile synthesis of 1,4-dideoxy-1,4-imino-l-ribitol (LRB) and (−)-8a-epi-swainsonine from d-glutamic acid

A facile synthesis of (−)-8a-epi-swainsonine 2 and 1,4-dideoxy-1,4-imino-l-ribitol (LRB) 4 has been achieved by using the versatile building block 3, which was available from cheap d-glutamic acid. The new forming stereogenic center in synthesis of 2 was constructed by highly selective reduction of the ketone 13 with Li(t-BuO)₃AlH in THF (dr=95:5).     

New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < −90 °C) followed by a quench with a slight excess of ClPPh₂ afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR₂ yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh₂)₂-2,5-(PR₂)₂-C₆F₂ (R = Ph (2a); R = ⁱPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh₂/PR₂ substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups.     

An efficient synthesis of 1,4-dideoxy-1,4-imino-d- and l-arabinitol and 1,4-dideoxy-1,4-imino-d- and l-xylitol from chiral aziridines

A highly efficient method for the synthesis of 1,4-dideoxy-1,4-imino-d- and l-arabinitol (d-AB1, 1 and l-AB1, 3) and 1,4-dideoxy-1,4-imino-d- and l-xylitol (d-DIX, 2 and l-DIX, 4) starting from commercially available chiral aziridines was developed. The general strategy employs a sequence involving two-carbon homologation, dihydroxylation, and regioselective aziridine ring opening/intramolecular five-membered iminosugar ring formation. The facile use of recrystallization to generate pure diastereomers makes the routes more amenable to large-scale synthesis.     

Polyhydroxylated pyrrolidines. Part 4: Synthesis from d-fructose of protected 2,5-dideoxy-2,5-imino-d-galactitol derivatives

The readily available 3-O-benzoyl-4-O-benzyl-1,2-O-isopropylidene-5-O-methanesulfonyl-β-d-fructopyranose (5) was straightforwardly transformed into its d-psico epimer (8), after O-debenzoylation followed by oxidation and reduction, which caused the inversion of the configuration at C(3). Compound 8 was treated with lithium azide yielding 5-azido-4-O-benzyl-5-deoxy-1,2-O-isopropylidene-α-l-tagatopyranose (9) that was transformed into the related 3,4-di-O-benzyl derivative 10. Cleavage of the acetonide in 10 to give 11, followed by regioselective 1-O-pivaloylation to 12 and subsequent catalytic hydrogenation gave (2R,3S,4R,5S)-3,4-dibenzyloxy-2,5-bis(hydroxymethyl)-2′-O-pivaloylpyrrolidine (13). Stereochemistry of 13 could be determined after O-deacylation to the symmetric pyrrolidine 14. Total deprotection of 14 gave 2,5-imino-2,5-dideoxy-d-galactitol (15, DGADP).     

Iron pentacarbonyl assisted photochemical route to 2,5- and 2,6-divinyl-substituted 1,4-benzoquinones from 1-ene-3-ynes

Photochemical reaction between the enynes, (Z)-1-methoxybut-1-ene-3-yne, 1 or isopropenyl acetylene, 2 with CO in presence of Fe(CO)₅ yields the 2,6- and 2,5-divinyl-substituted 1,4-benzoquinones: 2,6-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (3, 42%), 2,5-bis{(Z)-2-methoxyvinyl}-1,4-benzoquinone (4, 31.5%), [{η²,η²:2,6-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (5, 45%), and {η²,η²:2,5-di(prop-1-en-2-yl)-1,4-benzoquinone}tricarbonyliron] (6, 65%).     

Synthesis and reactivity of pyrrolo[3,2-d][1,3]oxazine-2,4-dione. Access to new pyrrolo[3,2-e][1,4]diazepine-2,5-diones

A convenient synthesis of pyrrolo[3,2-d][1,3]oxazine-2,4-dione 4 is described and its reactivity towards various nucleophiles studied. The regioselective ring opening of anhydride 4 or its N-alkylated analog 25 in the presence of alanine or proline afforded, respectively, imidazolidinedione 22 and N-protected pyrrolo[3,2-e][1,4]diazepines 30 and 31 in a one-pot process. In a last part of this study, an alternative route to produce a library of eight non protected pyrrolo[3,2-e][1,4]diazepine-2,5-diones 35a–h is described to overcome the limited reactivity of anhydride 4.     

Syntheses, structures, and photoluminescence of three-dimensional lanthanide coordination polymers with 2,5-pyridinedicarboxylic acid

Four new open-framework coordination polymers of lanthanide 2,5-pyridinedicarboxylates, with the formulas Pr2(pydc)₃(H₂O)₂ (1), Ln(pydc)(Hpydc) (Ln=Tb (2), Er (3), Eu (5)), and Gd(pydc)(nic)(H₂O) (4) (H₂pydc=2,5-pyridinedicarboxylic acid, Hnic=nicotinic acid), have been hydrothermally synthesized and four of them (except Eu (5)) have been structurally characterized. Complex 1 consists of two types of ligand-binding modes contributing to link the PrO₇N(H₂O) polyhedral chains to three-dimensional (3D) open-framework architecture. Complexes 2 and 3 are isostructural and feature unique 3D cage-like supramolecular frameworks remarkably different from that of 1, owing to the different ligand-bridging pattern. Complex 4, however, has the distinct 3D open-framework architecture due to the presence of unexpected nicotinate ligands, which may be derived from pydc ligands via in-situ decarboxylation under the hydrothermal condition.     

A microwave-assisted synthesis of triphenodioxazines [TPDOs]

A convenient and efficient method for the synthesis of triphenodioxazines [TPDOs] 1 by oxidative cyclisation of 2,5-bis-(arylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-diones 6 using potassium persulfate as the oxidising agent in 95?97% sulfuric acid triggered by microwave irradiation is described.     

Preparation of 1,1-disubstituted silacyclopentadienes

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.     

Polyhydroxylated pyrrolidines, III. Synthesis of new protected 2,5-dideoxy-2,5-iminohexitols from d-fructose

The readily available 3-O-benzoyl-4-O-benzyl-1,2-O-isopropylidene-β-d-fructopyranose (6) was straightforwardly transformed into 5-azido-3-O-benzoyl-4-O-benzyl-5-deoxy-1,2-O-isopropylidene-β-d-fructopyranose (8), after treatment under modified Garegg's conditions followed by reaction of the resulting 3-O-benzoyl-4-O-benzyl-5-deoxy-5-iodo-1,2-O-isopropylidene-α-l-sorbopyranose (7) with lithium azide in DMF. O-debenzoylation at C(3) in 8, followed by oxidation and reduction caused the inversion of the configuration to afford the corresponding β-d-psicopyranose derivative 11 that was transformed into the related 3,4-di-O-benzyl derivative 12. Cleavage of the acetonide of 12 to give 13 followed by O-tert-butyldiphenylsilylation afforded a resolvable mixture of 14 and 15. Compound 14 was transformed into (2R,3R,4S,5R)- (17) and (2R,3R,4S,5S)-3,4-dibenzyloxy-2′,5′-di-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (18) either by a tandem Staudinger/intramolecular aza-Wittig process and reduction of the resulting intermediate Δ²-pyrroline (16), or only into 18 by a high stereoselective catalytic hydrogenation. When 15 was subjected to the same protocol, (2S,3S,4R,5R)- (21) and (2R,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (22) were obtained, respectively.     

Syntheses and crystal structures of di- and triorganotin derivatives with 2,5-dimercapto-1,3,4-thiodiazole

A series of organotin(IV) complexes with 2,5-dimercapto-1, 3, 4-thiodiazole (HHdmt) of the type (R_nSnCl_m)₂(dmt) (m=0, n=3, R=Ph 1, PhCH₂2, n-Bu 3; m=1, n=2, R=Ph 4) and [R₂Sn(dmt) · L]_n (L=0.5C₆H₆, R=CH₃5; L=0, n=5, R=n-Bu 6) have been synthesized. All complexes 1-6 were characterized by elemental analysis, IR, ¹H and ¹³C NMR spectra. And except for 3, complexes 1, 2, 4, 5 and 6 were also determined by X-ray crystallography. The tin atoms of complexes 1, 2, 3 and 4 are all five-coordinated. The geometries at tin atoms of 1, 2, 3 and 4 are distorted trigonal bipyramidal. The tin atoms of complexes 5 and 6 are six-coordinated and their geometries are distorted octahedral.     

Stereoselective synthesis of (2R,3S,4S)-3-hydroxy-4-methyl-2-tetradecyl-4-butanolide starting from 2,5-anhydro-d-mannitol

A novel approach to natural β-hydroxy-γ-lactone 2 from 2,5-anhydro-d-mannitol (1) is described. The key reactions in this synthesis include stereoselective methylation of aldehyde 3 with lithium dimethylcuprate, an intramolecular radical cyclization of seleno carbonate 11 and an intermolecular cross-metathesis of 3-allyl-4-hydroxy-γ-lactone 16 with 1-tridecene.     

2(H)-1,4-Oxazin-2-ones as ambident azadienes

3,5-Dichloro-6-phenyl-2(H)-1,4-oxazin-2-one 3, 5-chloro-3,6-dimethyl-2(H)-1,4-oxazin-2-one 4, 5-chloro-6-methyl-3-phenyl-2(H)-1,4-oxazin-2-one 5 and 5-chloro-3,6-diphenyl-2(H)-1,4-oxazin-2-one 7, are ambident azadienes reacting efficiently and selectively with both electron rich and electron poor dienophiles.     

Synthesis and ring opening reactions of 2-glyco-1,4-dimethyl-3-nitro-7-oxabicyclo[2.2.1]hept-5-enes

The high-pressure asymmetric Diels-Alder reactions of d-galacto- (1a) and d-manno-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitrohept-1-enitol (1b) with 2,5-dimethylfuran (2) afforded mixtures of cycloadducts, from which the (2S,3R)-3-exo-nitro (3a and 3b), (2R,3S)-3-exo-nitro (4a and 4b), and (2R,3S)-1′,2′,3′,4′,5′-penta-O-acetyl-1′-C-(1,4-dimethyl-3-endo-nitro-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl)-d-galacto-pentitol (5b) were isolated pure. Deacetylation of these compounds led to new chiral mono-, bi-, and tricyclic ethers, being their asymmetric centers arising from the chiral inductor used in the cycloaddition reaction. A ring opening mechanism through a 1-nitro-1,3-cyclohexadiene intermediate has been proposed.     

The highly regiospecific synthesis and crystal structure determination of 1,1′-2,5′ substituted ring-locked ferrocenes

1,1′-Ferrocene biscarboxaldehyde (1) has been prepared and the aldehyde groups were subsequently protected with acetal groups to produce 1,1′-bisacetalferrocene (2). A ring-locked ferrocene was synthesised by further derivatisation of the cyclopentadiene rings at the 2,2′ positions with phosphine substituents to produce 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene (3), which was subsequently coordinated to either a nickel chloride (5) or nickel bromide (6) metal centre. The ring-locked ferrocene complexes produced 2,5′-bis-(acetal)-1,1′-diphenylphosphinoferrocene substitution patterns. The acetal protecting groups of 2,2′-bis-(acetal)-1,1′-diphenylphosphinoferrocene were removed to produce 1,1′-bis-carboxaldehyde-2,2′-diphenylphosphinoferrocene (4). The Cp rings of 1,1′-bisacetalferrocene were also further derivatised at the 2,2′ positions with a silane to produce the ring-locked 1,1′-siloxane-2,5′-bisacetalferrocenophane (7). The acetal protecting groups were removed from this to produce 1,1′-siloxane-2,5′-ferrocenophanecarboxaldehyde (8). For both the phosphine and siloxane electrophiles, the substitution on the Cp rings gives chiral products (obtained as racemic mixtures). Due to the highly regioselective nature of the reaction and diastereoselectivity in the products only C₂-symmetric compounds were observed without the presence of meso diastereoisomers. Subsequent ring-locking forced the Cp rings to rotate, leading to 1,1′-ring-locked ferrocenes with 2,5′-arrangement of the acetal groups (i.e. on opposite faces of the ferrocene unit).     

Lipase-mediated synthesis of enantiomeric 2,5,6-trideoxy-2,5-iminohexitols

Syntheses of 2,5,6-trideoxy-2,5-imino-d-alditol (2, 6-deoxy-DADP) and its enantiomer (3) from tri-orthogonally protected derivatives of DADP have been developed employing lipase-mediated kinetic desymmetrization and protecting group manipulations. Thus, and as an example, the starting DADP derivative (4) was transformed into a new symmetrical 2,5-bis(hydroxymethyl)pyrrolidine (6) by sequential N-protection and bis-O-desilylation. The lipase-mediated desymmetrization of 6 was best carried out under acetylation conditions to give (2R)-acetyloxymethyl derivative 7. The absolute configuration and ee of 7 were unambiguously established by chemical correlation with a homochiral sample. Compound 7 was straightforwardly transformed into the target 2,5,6-trideoxy-2,5-iminohexitol 3.     

Synthesis and elucidation of absolute stereochemistry of salaprinol, another thiosugar sulfonium sulfate from the ayurvedic traditional medicine Salacia prinoides

Synthesis and elucidation of absolute stereochemistry of salaprinol (3) isolated from the root and stems of Salacia prinoides, which has been used for the treatment of diabetes in India, Sri Lanka, and Southeast Asia countries, is described. Compound 3 and its 2′-epimer, epi-salaprinol (epi-3) were synthesized via the coupling reaction of a cyclic sulfate, 2-O-benzylglycerol 1,3-cyclic sulfate (5), with a thiosugar, 1,4-dideoxy-1,4-epithio-d-arabinitol (6), as the key reaction, and S configuration of the asymmetric center in the side chain of 3 was elucidated by the X-ray crystallographic analysis.