209. Thioalkylation of Meldrum’s Acid: Protected Alkylidene Derivatives of lsopropylidene Malonate

Thioalkylated Meldrum’s acid is easily available by treatment of Meldrum’s acid with an aldehyde and thiophenol in the presence of catalytical amounts of piperidinium acetate (-+A, Table 1). The adducts 1 4 are crystalline, stable compounds and they can be caused to react directly with nucleophiles and dienes (see 3+7-12, Scheme I). The regeneration of the parent olefin is effected thereby by simply dissolving the adduct under neutral or basic conditions. Extension of this method to thiocarboxylic acids allowed the preparation of the corresponding formaldehyde derivatives 13 and 15 (Table 3). Introduction.- Isopropylidene alkylidenemalonates i [ 11 have achieved considerable interest as highly reactive MichueE acceptors [2], electron-deficient dienophiles [3], strongly polarized heterodienes [4], and as precursors of the corresponding saturated compounds [5] as well as of methylene ketenes [6]. I ii ii