Thioalkylation of Meldrum's Acid: Protected alkylidene derivatives of isopropylidene malonate

Thioalkylated Meldrum's acid is easily by treatment of Meldrum's acid with an aldehyde and thiophenol in the presence of catalytical amounts of piperidinium acetate (→1–6, Table 1). The adducts 1–6 are crystalline, stable compounds and they can be caused to react directly with nucleophiles and dienes (see 3→7–12, Scheme 1). 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).