Srinivasachari Rajappa

Synthesis of 1,1-diamino-2-thioacylethylenes: A novel C-thioacylation by the Willgerodt-Kindler reaction

Abstract A novel C -thioacylation reaction is described. Reaction of aromatic or heterocyclic aldehydes with 1-alkyl-2-methyl-1,4,5,6-tetrahydropyrimidine or 1-alkyl-2-methylimidazolidine in the presence of sulphur leads to the thioacylketeneaminals 6 , 10 or 12 in low to moderate yields. The structure of 6e was proved by S -methylation to 7e and acid-hydrolysis to the known 8e . Oxidative cyclization of 6 leads to the isothiazolo[2,3- a ] pyrimidinium salts 13 .

SYNTHESIS AND CHARACTERIZATION OF 1-AMINO-4-METHYLTHIO-2-NITRO-1,3-BUTADIENES

Treatment of 3-nitrothiophene with prim. and sec. amines, followed by S-methylation leads to (Z,Z)-1- amino-4-methylthio-2-nitro-1,3-butadienes (3). Oxidation of these with LTA yields a mixture of the 2-methylthio-4-nitropyrroles (6) and the acetoxylated butadienes (8).

Unique zeolite-catalyzed synthesis of nitroketene S,N-acetals

Abstract Dimethyl carbonimidodithioates (4a–g, 7a–c) derived from various primary amines and amino acid esters [glycine, (L)-alanine and (L)-phenylalanine] have been condensed with nitromethane in the presence of the rare-earth exchanged zeolite RE(70%)Na Y to give the S,N-acetals (5a–g, 8a–c). Mercuric chloride catalyzed hydrolysis of these (8a–c) has led to the nitroacetyl derivatives (9a–c). The glycine derivative (7a) gives a dimeric product (11) when heated alone with the zeolite.

Conformational preferences of α-functionalised keten-S,N-acetals: Potential role of SO and SS interactions in solution

PMR spectra of carbonyl compounds 2a-k reveal significant variations in the population of E and Z isomers on changing the solvent from CDCl3 to DMSO-d6. In non-polar media, the intramolecular N-H…. O hydrogen bonded form is exclusively observed. In DMSO-d6, the alternative Z form is also populated. A similar conformational switch is also noted in the corresponding thiones. Different interpretations are critically analysed. The most consistent explanation is suggested to involvean interplay of N-H….X hydrogen bonding and S…X attractive interaction (X = O,S) in these systems. Ab initio calculations support this interpretation.

A novel synthesis of 5-acylaminobenzimidazole-2-carbamates : intramolecular regioselective addition to quinone-imides.

Abstract Oxidation of N′,N″ -biscarbomethoxy-N-(4-acylamino) phenylguanidines with lead tetraacetate has given novel 5-acylaminobenzimidazole-2-carbamates by a process involving regioselective cyclization of intermediate quinoneimides.

Oxidative nucleophilic substitution of hydrogen by primary amines in 2-nitrobenzo[b]thiophene

2-Nitrobenzo[b]thiophene on treatment with primary amines and CAN in aq MeCN undergoes oxidative nucleophilic substitution reactions to give 2-nitro-3-aminobenzo[b]thiophenes as crystalline solids.

Facile acid catalyzed ring cleavage of N-acylated lactams

Abstract N-Alkoxycarbonyl and N-arylsulfonyl lactams ( 1a - e ) were prepared and converted to the corresponding acyclic products ( 2a - h ) by acid catalyzed cleavage of the lactam ring in good yields and excellent regioselectivity.

Conversion of carbonimidodithioates into unsymmetrical Di- and Tri- substituted ureas including urea dipeptides

Selective hydrolysis of carbonimidodithioates (3) leads to the thiocarbamates (4), which can be easily transformed to the unsymmetrical ureas (5) by treatment with the appropriate amines. This constitutes a synthesis of ureas without the use of phosgene or carbon monoxide.

Synthesis of novel cyclic hydroxamic acids

Abstract The nitroacetyl ( S )-proline esters ( 1,3,5 ) are reduced by zinc-NH 4 Cl to the hydroxylamine stage and cyclized to provide the novel chiral bicyclic hydroxamic acids ( 2,4,6 ). Michael addition of allyl acrylate on nitroacetic acid derivatives followed by Pd(0) catalyzed intramolecular allyl transfer and subsequent reduction of the nitro group yielded a novel class of cyclic hydroxamic acids related to pyroglutamic acid.

Conversion of thiocarbamates to carbamates

Abstract Treatment of methyl N-methylthionocarbamate (2a) with a catalytic amount of iodine or conc. H2SO4 results in the unexpected formation of the isomer, methyl N-methylthiolcarbamate (3a) in 90% yield. This has subsequently been transformed into methyl N-methylcarbamate (4a), by sodium methoxide. A curious transformation of methyl N-methyldithiocarbamate (1a) to (4a) on prolonged treatment with sodium methoxide is also discussed.