A highly stereoselective synthesis of aldols employing the Reformatsky reaction of 3-(2-bromopropionyl)-2-oxazolidone derivatives with various aldehydes

The title reactions of sterically crowded 2-oxazolidone derivatives with achiral aldehydes in the presence of zinc dust were found to give various 2,3- -aldols as major products (at most, 2,3- :2,3- =98:2). While a 2,3- -3,4- -aldol could be similarly produced in a highly stereoselective manner, application of the explored reaction to asymmetric synthesis of optically active 2,3- -aldols was found to be unpromising.     

A highly stereoselective synthesis of α,β-unsaturated oxazolines

Lithiated 2,4,4-trimethyl-2-oxazoline 2a and 2-chloromethyl-4,4-dimethyl-2-oxazoline 2b react smoothly with a number of nitrones 3 to produce α,β-unsaturated oxazolines 6 and 7 highly stereoselectively.     

Synthesis of 2-(α-fluorobenzyl)benzimidazole derivatives

New 2-(α-fluorobenzyl)benzimidazole derivatives have been prepared. Fluorination was carried out from benzylic alcohols using 2-chloro-1,1,2-trifluorotriethylamine reagent. The scope and the rates of formation of the resulting products are dependent on the nature of the substituents. Physical data, ¹H and ¹⁹F NMR chemical shifts of the hydroxy and fluorine compounds are given.     

A highly stereoselective synthesis of chiral alpha-amino-beta-lactams via the Kinugasa reaction employing ynamides

A highly stereoselective synthesis of chiral alpha-amino-beta-lactam through an ynamide-Kinugasa reaction is described. In addition, a mechanistic model is illustrated here to rationalize the observed diastereoselectivity, which depends on both the initial [3 + 2] cycloaddition step and the subsequent protonation for which both are highly selective.     

A convenient synthesis of certain 1-(β-D-ribofuranosyl)benzotriazoles

The synthesis of 5,6-dichloro-1-(β-D -ribofuranosyl)benzotriazole ( 4a ), 5,6-dimethyl-1-(β-D -ribofuranosyl)benzotriazole ( 4b ) and 1-(β-D -ribofuranosyl)benzotriazole ( 4c ) in good yield has been accomplished by the condensation of the appropriate 1-trimethylsilylbenzotriazole ( 1a, 1b , and 1c ) with 2,3,5-tri-O-acetyl-D -ribofuranosyl bromide (2) followed by subsequent deacetylation of the reaction products. The assignment of anomeric configuration and site of glycosidation for all nucleosides reported is discussed.     

The synthesis of 2-chloro-1-(β-D-ribofuranosyl)benzimidazole and certain related derivatives

The synthesis of 2-chloro-1-(β-D-ribofuranosyl)benzimidazole (4b) has been accomplished by a condensation of 2-chloro-1-trimethylsilylbenzimidazole (1) with 2,3,5-tri-O-acetyl-D-ribofuranosyl bromide (2) followed by subsequent deacetylation. Nucleophilic displacement of the 2-chloro group has furnished several interesting 2-substituted-1-(β-D-ribofuranosyl)benzimidazoles. 1-(β-D-Ribofuranosyl)benzimidazole (5) and 1-(β-D-ribofuranosyl)benzimidazole-2-thione (6) were prepared from 4b and 6 was also prepared by condensation of 2 with silylated benzimidazole- 2-thione (3). Alkylation of 6 furnished certain 2-alkylthio-1-(β-D-ribofuranosyl)benzimidazoles and oxidation of 6 with alkaline hydrogen peroxide produced 1-(β-D-ribofuranosyl)benzimidazole-2-one (9). The assignment of anomeric configuration for all nucleosides reported is discussed.     

Studies on furan derivatives IV. A simple preparation of α-substituted β-(5-nitro-2-furyl)ethynyls from α-substituted β-(5-nitro-2-furyl)vinylamines

α-Substituted β-(5-nitro-2-furyl)ethynyls were conveniently prepared by the deamination of α-substituted β-(5-nitro-2-furyl)vinylamines. Also the application of this reaction toward α,β-bis(p-nitrophenyl)vinylamine was examined and afforded α,β-bis(p-nitrophenyl)ethynyl as the main product.     

The stereoselective synthesis of β‐haloenol phosphates—A reinvestigation of the reaction of α‐haloketones with diethyl phosphite

A new pathway for the reaction involving an α‐haloketone and a dialkyl phosphite has been suggested, It offers a highly stereoselective synthetic procedure leading to β‐haloenol phosphates in one‐pot reactions that take place in good yields. However, normal Pudovik reaction products were formed when the reaction was carried out using a relatively small amount of base. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 55–59, 1999     

A novel stereoselective synthesis of (Z)‐α‐arylsulfanyl‐α,β‐unsaturated ketones via Stille coupling of (E)‐α‐arylsulfanylvinylstannanes with acyl halides

(E)‐α‐Arylsulfanylvinylstannanes react with acyl halides in the presence of a catalytic amount of Pd(PPh₃)₄ and CuI cocatalyst to give stereoselectively the corresponding (Z)‐α‐arylsulfanyl‐α,β‐unsaturated ketones in good yields. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:218–223, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20536     

A convenient synthesis of (z)-3-(α-alkoxycarbonyl-α-cyanomethylene)-2-oxo-1,2,3,4-tetrahydroquinoxalines and related compounds

(Z)-3-(α-Alkoxycarbonyl-α-cyanomethylene)-2-oxo-1,2,3,4-tetrahydroquinoxalines 3 and (Z)-3-(α-alkoxycarbonyl-α-cyanomethylene)-3,4-dihydrobenzo[g]quinoxalin-2(1H)-ones 5 possessing various alkoxycarbonyl groups were prepared in good yields directly from the reaction of dialkyl (E)-2,3-dicyanobutendioates 1 with o-phenylenediamine ( 2 ) or with 2,3-diaminonaphthalene ( 4 ), respectively. Furthermore, 2,3-diaminopyridine ( 6 ) and 3,4-diaminopyridine ( 7 ) were reacted with the diethyl ester 1b to give (Z)-2-(α-cyano-α-ethoxycarbonylmethylene)-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one ( 8 ) and (Z)-3-(α-cyano-α-ethoxycarbonylmethylene)-3,4-dihydro-1H-pyrido[3,4-b]pyrazin-2-one ( 9 ), respectively. The structural studies of 3, 5, 8 , and 9 were carried out by nmr experiments in some details.     

Short synthesis of tryptophane and β-carboline derivatives by reaction of indoles with N-(diphenylmethylene)-α,β-didehydroamino acid esters

The ethylaluminum dichloride catalyzed Michael-type addition of indoles 1a-h to the N-(diphenylmethylene)-α,β-didehydroamino acid esters 2a-c allows a new synthesis of β-methyltryptophanes 41,m and a new route for 1,1-diphenyl-3-carbalkoxy-1,2,3,4-tetrahydro-β-carbolines 5a-m.     

β-Carbolines derived from β-methyltryptophan and a stereoselective synthesis of (2RS,3SR)-β-methyltryptophan methyl ester

The methyl ester of isomer A of β-methyltryptophan (2SR,3RS; 2A ) was stereoselectively prepared by an efficient modified method through the reaction of a-methyl-N-(1-Methylethyl)-1H-indole-3-methanamine ( 3 ) with methyl nitroacetate to give the desired nitro compound as a mixture of two racemates 5A , and 5B. During the recrystallization process epimerization occurred and only racemate 5A crystallized out. Catalytic hydrogenation of 5A in the presence of acid stereoselectively yielded the desired amino acid ester 2A. Pictet-Spengler condensation of 2A with aldehydes under aprotic conditions followed by dehydrogenation gave excellent yields of β-carbolines 7a-i , (R = methyl, ethyl, acetyl, phenyl, pyridine-2-yl, furan-2-yl, quinoline-2-yl, styryl, phenethyl). Also β-carbolines 7a,b,i were synthesized by the Pictet-Spengler condensation of (3-meth-yltryptophan under acidic aqueous conditions followed by esterification and dehydrogenation.     

The synthesis of 1-substituted-2-(β-dimethylaminoethyl)benzimidazoles

2-(β-Dimethylaminoethyl)benzimidazoles have been prepared by the reduction of the corresponding 2-benzimidazole-N,N-dimethylacetamides. Condensation of ethyl cyanoacetate with N-benzyl or phenyl-o-phenylenediamines led to N-cyanoacetyl-N'-substituted-o-phenylenediamines, the structure of which were assigned from u.v. and n.m.r. data. An improved synthesis of benzimidazole - 2 - acetic acid derivatives, from substituted ethyl acetimidates and o-phenylenediamines, is described. Dimerisation of 1-phenyl-benzimidazole occurs in the presence of phenyllithium.     

The synthesis of β-heteroarylamino-α,β-dehydro-α-amino acid and β-heteroarylamino-α-amino acid derivatives

From heteroarylaminomethyleneoxazolones 4 , obtained from N-heteroarylformamidines 2 and 2-phenyl-5-oxo-4,5-dihydro-1,3-oxazole ( 3 ), the following β-heteroarylamino-α,β-dehydro-α-amino acid derivatives were prepared: methyl 8 and ethyl esters 9 , amides 10 and 11 , hydrazides 12 , and azides 15 . By catalytic hydrogenation the compounds 4 were converted into β-heteroarylamino substituted amides 18 and β-heteroarylamino-α-amino acids 20 .