Ketene, dithioacetal, vinylogous

B.V. A R(C=0)CH2CH2CH2+ Equivalent. In this umpolung equivalent, the potentially positive center is even further removed from the carbonyl (see 342 in Table 8.18). This umpolung equivalent is best achieved by reaction of a nucleophile with a vinylogous ketene dithioacetal such as 395.376 initial reaction of... 

Ketene Dithioacetal Formation. These versatile intermediates arise from 1,3-dithiane anions by elimination (eq 8) or vinylogous alkylation (eq 4), and by condensation of carboxylic acid derivatives with (1) (eq 13). Ketene dithioacetals derived from lactones can cyclize to give dithio orthoesters, which can be selectively deprotected (eq 16). ... 

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