Cyclocondensation of 2-lithiomethylthiazoles and 2-lithiomethylthiazoline with α-oxoketene dithioacetals: synthesis of substituted and annelated thiazolo- and dihydrothiazolo[3,2-a]pyridinium compounds
The oxoketene dithioacetals 1 undergo regioselective 1,2-addition with 2-lithiomethyl-4-methylthiazole (2a) and 2-lithiomethylthiazoline (3) to afford the carbinol acetals 4 which on borontrifluoride etherate assisted cyclization yield the corresponding substituted and annelated 3-methyl-5- methylthiothiazolo[3,2-a.] pyridinium tetrafluoroborates (5a-g, 8a,b,10,12) and the dihydro derivatives (23-25)
Cyclocondensation of oxoketene dithioacetals with 3-aminopyrazoles: a facile highly regioselective general route to substituted and fused pyrazolo ]pyrimidines
3-amino-5-methylthio-4-phenylpyrazole (1b) withα-oxoketene dithioacetals (2a-j derived from acyclic active methylene ketones affords 5-methylthio-6,7-substituted pyrazolo[1,5-a]pyrimidines (3a-J) exclusively. The reaction was found to be equally successful for the synthesis of 7-styryl,7-(4-aryl-1,3-butadienyl) and 7-(6-aryl-1,3,5-hexatrienyl)pyrazolopyrimidines (7a-f) from the respective enoylketene dithioacetals (6a-f)
A Facile Synthesis of 2-Amino-4-alkoxy-6-styryl- and 2-Amino-4-alkoxy-6-(4-aryl-1,3-butadienyl)-pyrimidines by Direct Cyclocondensation
作者:L. W. Singh、A. K. Gupta、H. Ila、H. Junjappa
DOI:10.1055/s-1984-30889
日期:——
Acid-induced ring opening of .alpha.-bis(methylthio)methylenealkyl cyclopropyl ketones: a novel route to substituted cyclopentanones through carbocationic cyclizations
Alpha-[Bis(methylthio)methylene]alkyl 2-styrylcyclopropyl ketones 10a-d,f and their higher enyl analogues 10e,g undergo acid-induced ring opening and carbocationic cyclizations to afford substituted cyclopentanone derivatives. The structures of these products depend on the reaction conditions and the nature of the substituent in the aryl ring. The methodology has been extended to the synthesis of 11-oxosteroid precursors 22 and 25.