Reaction of lithioamino anions with α-oxoketene dithioketals: an improved and a new general method for the synthesis of α-oxoketene S, N- and N, N-ketals

A new method has been developed for the preparation of α -oxoketene S,N- (A) and N,N-(B) ketals starting from α -oxoketene dithioketals by employing mild conditions. Thus, lithioamino anions 2a-c, 4 and 6 are treated with α -oxoketene dithioketals 1 to afford the corresponding S,N-ketals 3a-j, 5a-j, 7a-e and N,N-ketals 8a,b in good yields. The scope and steric orientations of the reaction have been investigated

Anionic [4 + 2] cycloaddition reactions of dihydropyrazolin-5-one dienolate with dienophiles: a novel approach for substituted and fused indazolones

Dihydropyrazolin-5-one dienolate 2 generated by deprotonation of 2,3-dimethyl-4-formyl-1-phenylpyrazolin-5-one (4-formylantipyrine) is shown to be an efficient anionic pyrazolone α -oxy-o-quinodimethane analog, which undergoes facile cycloaddition with a variety of dienophiles to give substituted indazolones in good yields after dehydration-dehydrogenation of cycloadducts

Direct synthesis of 2-(cycloalkylamino)-3,4-substituted thiophenes via selective deprotonation-cyclization of aroyl ketene N,S-acetals

Acyclic and cyclic aroyl ketene N,S-acetals undergo regioselective deprotonation-cyclization via dipole stabilized carbanion in the presence of LDA/THF to afford the corresponding 2-(cycloalkylamino)-4-aryl or 3,4-annelated thiophenes in moderate to good yields

Lewis acid-induced rearrangment of α-[bis(methylthio)methylene]ethyl-2-styrylcyclopropylcarbinols: unexpected formation of a novel bicyclo[3.2.1]octadiene framework

The α-[bis(methylthio)methylene]ethyl-2-styrylcyclopropylcarbinols 9a-c undergo a simple but unexpected skeletal rearrangement in the presence of stannic chloride in nitromethane to afford bicyclo[3.2.1]octadiene derivatives 10a-c exclusively in good yields. The structure of 10a was conclusively elucidated by X-ray diffraction studies. A possible mechanism governing the formation of 10 is proposed

Molecular Diversity through Novel Organosulfur Synthons: Versatile Templates for Heterocycle Synthesis

This review highlights some of our recent work on design and development of new synthetic methods for diverse classes of heterocycles employing novel organosulfur synthons i.e. polarized ketene dithioacetals, N, S-acetals, ?-oxodithioesters and 2,3-(hetero)aryl-3-(methylthio)acrylonitriles, easily accessible from a wide range of active methylene compounds

Reformatskii reaction on α-oxo ketene dithioacetals: synthesis of substituted and fused ethyl 2-hydroxy-6-(methylthio)benzoates, 6-(methylthio)pyran-2-ones, and 6-(methylthio)-2(1H)pyridone derivatives

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Heteroaromatic annulation studies on 10,11-dihydro-11-[bis(methylthio)methylene]dibenzoxepin-10-one: a facile access to novel dibenzoxepino[4,5]-fused heterocycles

10,11-Dihydro-11-[bis(methylthio)methylene]dibenzoxepin-10-one has been shown to be a useful three carbon synthon for the efficient regiospecific annulation of a variety of five- (pyrazoles, isoxazoles, thiophene, and γ-lactone) and six-membered (pyrimidines, pyridone and pyridines) heterocycles by cyclocondensation with heterobinucleophiles such as hydrazine, hydroxylamine, dimethylsulfonium methylide, guanidine, thiourea, cyanoacetamide, and substituted β-lithioaminoacrylonitrile

Polarized ketene dithioacetals. Part 26. Studies on base-catalysed rearrangements of 3,3-bis(alkylthio)-2-methyl-1-arylprop-2-en-1-ones and 3,3-bis(methylthio)-2-benzyl-1-phenylprop-2-en-1-one

3,3-Bis(alkylthio)-2-methyl-1-arylprop-2-en-1-ones (1a-e) undergo facile rearrangement in the presence of sodium hydride in dimethylformamide to give the corresponding 3-alkylthio-2-alkylthiomethylacrylophenones (2a-e), respectively. Similarly 3,3-bis(methylthio)-2-benzyl-1-phenylprop-2-en-1-one (13) under similar conditions yielded the rearranged product, the chalcone (14) and the acrylophenone (15), in addition to two more products, β-methylthiochalcone (16) and the propenone (17). The mechanisms governing these transformations have been studied and it has been shown that the 1,3-RS shift in the dithioacetal intermediate (19) involves intermolecular participation of thiolate anion rather than a concerted process. A probable mechanism involving the solvent equilibrated enolate anion (27) formed by Michael addition of thiolate anion to (19) or the phenyl derivative (26) has been suggested for the rearrangement of (19) to the products (2) and of (26) to either compound (14) or (15). Also, the formation of products (16) and (17) is explained through oxidative cleavage of the carbanions (28) and (31) respectively

Polarised ketene dithioacetals. Part 50. Reactions of α-aroyl-α-bromoketene dithioacetals with hydrazine hydrate: formation of rearranged pyrazoles

The reactions of α-aroyl-α-bromoketene dithioacetals (2a-c) with hydrazine hydrate yields unexpected pyrazoles, i.e. 3(5)-aryl-5(3)-4-bis(alkylthio)pyrazoles (7), 3(5)-arylpyrazoles (8), and 4-amino-5(3)alkylthiopyrazoles (9) in varying yields. The corresponding S-ethyl-α-bromoketene dithioacetal (2d) gave only the bis(ethylthio)pyrazole (7d) and 4-amino-4(3)-ethylthiopyrazole (9d) under similar conditions. The reactions of cyclic α-bromo ketene dithioacetals (2e-g) with hydrazine hydrate on the other hand afforded only the [1,4]dithiinopyrazole derivatives (7e-g) in high yields. The probable mechanisms for the formation of the pyrazoles (7)-(9) have been suggested