A regioselective approach to 5-substituted-3-amino-1,2,4-triazines

Nucleophilic displacement of readily available alpha,alpha-dibromoketones with excess morpholine gave the corresponding ketoaminals, which upon condensation with aminoguanidine in MeOH in the presence of AcOH afforded 5-substituted-3-amino-1,2,4-triazines in >95% regioselectivity and 45-76% isolated yield. [reaction: see text]     

A general approach for the synthesis of 5-substituted-4-amino-pyrrolidin-2-ones and 5-substituted-4-amino-3-pyrrolin-2-ones

Short stereoselective syntheses of both 5-substituted-4-amino-pyrrolidin-2-ones and 5-substituted-4-amino-3-pyrrolin-2-ones from natural α-amino acids are described.     

A novel and highly regioselective approach to 5-methoxy-6-substituted-3-sulfonyl-delta-enlactams from 5-methoxy-3-sulfonyl glutarimide: synthesis of cis-2-substituted-3-piperidinols

A convenient method for the preparation of 5-methoxy-6-substituted-3-sulfonyl-delta-enlactams via regioselective nucleophilic addition to 5-methoxy-3-sulfonyl glutarimide is described. Formal syntheses of L-733,060, CP-99,994, and cassine are also reported.     

A convergent organoiron approach to steroid synthesis

The reaction of tricarbonyl (4-methoxy-1-methylcyclohexadienyl)iron hexafluorophosphate (1) with the keto ester nucleophile 5 to give complexes 6 and 7, and conversion of 6 in eight steps, via the enone 8a, to a D-homosteroid 11 is described.     

A modular approach to the synthesis of 1,4,5-substituted-2-aminoimidazoles

Diversified 1,4,5-substituted-2-aminoimidazoles were rapidly assembled via sequential N–H insertion and Grignard addition to α-diazoesters. Lead compounds were identified as antibiotics against Gram-positive bacteria with an MIC value as low as 2 μg/mL.     

A convergent approach to the synthesis of multimetallic dithiolene complexes

Controlled base hydrolysis of one or both of the protected 1,2-dithiolene chelates of 1,3,5,7-tetrathia- s-indacene-2,6-dione (OCS 2C 6H 2S 2CO) enables the stepwise synthesis of di- and trimetallic complexes with 1,2,4,5-benzenetetrathiolate as the connector. Treatment of OCS 2C 6H 2S 2CO with MeO (-), followed by [NiBr 2(dcpe)] [dcpe = 1,2-bis(dicyclohexylphosphino)ethane], yields [(dcpe)Ni(S 2C 6H 2S 2CO)] ( 4). The reaction of 4 with EtO (-), followed by [MX 2(dcpe)] (X = halide), yields [(dcpe)Ni(S 2C 6H 2S 2)M(dcpe)] [M = Ni ( 5a), Pd ( 5b)]. Deprotection of the 1,3-dithiol-2-one group of 4, followed by introduction of (1)/ 2 equiv of MX 2 and then I 2, yields the neutral trimetallic compounds [(dcpe)Ni(S 2C 6H 2S 2)] 2M [M = Ni ( 6a), Pt ( 6b)]. Tetrahedralization at nickel is observed in 5a, which density functional theory calculations attribute to second-order Jahn-Teller effects, while 6a and 6b display an end-to-end folding of approximately 46 degrees . A color darkening is observed in moving from 4 to compounds 6 due to the increasing size of the conjugated metal-organic pi system. Intense, broad absorptions in the near-IR are observed for 6a and 6b.     

A convergent approach to the formal total synthesis of hemibrevetoxin B

A convergent synthesis of the key synthetic intermediate of hemibrevetoxin B was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis.     

A simple convergent approach to the synthesis of the antiviral agent virantmycin

[structure: see text] The antiviral agent (+/-)-virantmycin has been synthesized from two simple building blocks (2 and 3) in eight steps, as outlined in Scheme 2.     

A concise approach to 5-substituted-4-pyrones from kojic acid

A concise approach to 5-substituted-4-pyrones is described. This approach is based on manipulation of the 5-hydroxy group of readily available kojic acid. A number of 5-substituted-4-pyrones were synthesized from kojic acid utilizing Heck reaction, Suzuki coupling and Stille coupling.     

A convergent approach to cyclopeptide alkaloids: total synthesis of sanjoinine G1.

A general strategy for the synthesis of cyclopeptide alkaloids containing an endocyclic aryl-alkyl ether bond has been developed featuring a key intramolecular S(N)Ar reaction. The importance of the N-terminal protective group in the realization of such a strategy is documented. From the appropriate amino acid constituents, the natural sanjoinine G1, a 14-membered para cyclophane, has been synthesized in seven steps with 21% overall yield.     

A novel approach to the synthesis of 5-trifluoromethyl-3-substituted pyrazoles

The 3-cyano-4-trifluoromethyl-6-phenyl or substituted phenyl 2(1H) pyridones (1) on reaction with hydrazine hydrate, gave exclusively in 5-trifluoromethyl-3-substituted pyrazoles (3) through a novel method. A possible mechanistic pathway for change in the site of nucleophilic attack due to the CF₃ group in 2(1H) pyridones is described.     

Free radical chemistry. Part 5. [1] A new approach to the synthesis of perfluorinated ethers

Fluorinations of the free-radical adducts of fluorinated alkenes, to ethers, over cobalt trifluoride are described and perfluorinated ethers are obtained at temperatures in excess of 400°C. The effect of structure on the formation of perfluoroethers is outlined.     

A new general approach to 4-substituted-3-halo-2-quinolones

A general procedure for the preparation of 4-substituted-3-halo-2-quinolones (halo = F, Cl, Br) utilizing 2-halo diethylphosphonoacetic acids (halo = F, Cl, Br) and o-aminophenylketones as the starting materials is described. The title compounds are obtained by an intramolecular Horner-Wadsworth-Emmons olefination of halogen-containing N-acyl-o-aminophenylketones. The transformation process is generally applicable under mild conditions.     

A new approach to the synthesis of 2-aminomethyl-3-phenyl-5-nitroindole

Bromination of 2-methyl-3-phenyl-5-nitroindoles has given previously unknown 2-bromoethyl-3-phenyl-5-nitroindoles, which were converted by the Delepine reaction into 2-aminomethyl-3-phenyl-5-nitroindoles. One of these (1-methyl-2-aminomethyl-3-phenyl-5-nitroindole) was also obtained by reductive amination of 1-methyl-2-formyl-3-phenyl-5-nitroindole by the Leuckart-Wallach reaction.     

A rapid synthesis of 2-aryl-5-substituted-2,3-dihydrobenzofurans

[reaction: see text] An effective strategy has been developed for the rapid and efficient one-pot synthesis of 2-aryl-5-substituted-2,3-dihydrobenzofurans from readily available o-nitrotoluenes and aromatic aldehydes. This strategy allows access to a structurally diverse array of products for further manipulation.     

A convenient synthesis of 5-substituted-7-β-D-arabinofuranosylpyrrolo[2,3-d]pyrimidines structurally related to the antibiotics toyocamycin and sangivamycin

4-Amino-7-(2,3,5-tri-O-benzyl-β-D-arabinofuranosyl)pyrrolo[2,3-d]pyrimidine-5-carbonitrile ( 6a ), prepared from 2-ethoxymethyleneamino-5-bromopyrrole-3,4-dicarbonitrile ( 4 ), was debenzylated with boron trichloride to give ara-toyocamycin ( 6b ). Further functional group transformation of 6b provided a route to 4-amino-7-β-D-arabinofuranosylpyrrolo[2,3-d]pyrimidine-5-thiocarboxamide (ara-thiosangivamycin, 7a ), and the corresponding 5-carboxamidoxime 8a and 5-carboxamidine 8b derivatives. Phosphorylation of unprotected 7a with phosphorus oxychloride gave ara-thiosangivamycin 5′-monophosphate ( 7b ). 2′-O-Acetyl-ara-thiosangivamycin ( 10b ) was prepared as a prodrug by acetylation of 9a , followed by deprotection of the t-butyldimethylsilyl groups under acidic conditions without acyl migration.     

Δ5-3β-取代-5-甾烯并取代[17,16-c]吡唑(异噁唑)啉-5''''-酮类化合物的合成

3β-取代-5-甾烯-17-酮与碳酸二甲酯经克莱森缩合所得产物再分别与肼或羟胺反应,合成了几种新的△5-3β-取代-5-甾烯并-1'-取代[17,16-c]吡唑啉-5'-酮和△5-3β-取代-5-甾烯并[17,16-c]异噁唑啉-5'-酮化合物,其结构均经元素分析,IR和1H NMR确证.     

A cyclopropane fragmentation approach to heterocycle assembly: a convergent synthesis of oxepanes

[reaction: see text] A cyclopropanol fragmentation approach to the synthesis of oxepanes has been developed. This convergent strategy condenses cyclopropyl diols with aldehydes to form an acetal, which is subsequently rearranged to furnish a keto-oxepane. The reaction has been developed as a one-pot procedure, utilizing sequential addition of Al(OTf)3 and TiCl4. Yields range from 50 to 70% for the sequence. A Zimmerman-Traxler transition state disposing substituents in equatorial positions is consistent with the observed formation of strictly cis products.     

A convergent approach to the mitomycin ring system

[structure: see text]. A novel stereoselective approach to the ring system of the mitomycins is described. The synthesis was based on a convergent strategy involving a stereocontrolled addition of a beta-phenyl silyl enol ether to a pyrroline N-acyliminium ion followed by an intramolecular palladium-catalyzed aryl triflate amination to afford the (9R*,9aR*)-tetrahydropyrrolo[1,2-a]indole ring system.