A new general synthesis of 3- and 3,4-substituted 4a–q, 3,4-annelated 7a–d and condensed tricyclic 9a–e thiophenes has been developed through Simmons-Smith reaction on the respective α-oxoketene dithioacetals. Extension of the reaction to α-cinnamoylketene dithioacetals 10a–e and its higher enyl analogs 13a–d, 15a–c gave the corresponding 3-styryl 11a–e and 3-di- and trienyl 14a–d, 16a–c thiophenes
Synthesis of Methyl 5-Aryl-3-oxo-4-pentenoates and Novel Substituted Cyclopentenones
作者:C. V. Asokan、S. Bhattacharji、H. Ila、H. Junjappa
DOI:10.1055/s-1988-27543
日期:——
The cinnamoyl- (1a-j) and (5-phenyl-2,4-pentadienoyl)- (1k) ketene dithioacetals are shown to undergo methanolysis in the presence of ether-boron trifluoride complex and mercury(II) chloride to the corresponding methyl 5-aryl-3-oxo-4-pentenoates 2a-j and 3-oxo-7-phenyl- 4,6-heptadienoate (2k), respectively, in good yields. However, the corresponding (2-methylcinnamoyl)ketene dithioacetals 3a-f, under identical reaction conditions, undergo Nazarov cyclization to give the corresponding substituted cyclopentenones 4a-f.
α-acylketene dithioacetals in refluxing benzene affords α-acetoxyketene dithioacetals as major products which could be hydrolyzed to α-diketone dithioacetals under mild alkaline conditions. Under similar oxidative conditions, α-cinnamoyl ketene dithioacetals yield 2-acetoxycyclopentenone derivatives through an interesting oxidative Nazarov cyclization involving intermediate α-acetoxy dithioacetals accompanied