Synthetic approaches to the thiathromboxanes. Part 1. Preparation of functionalised dihydrothiopyrans

A hetero-Diels–Alder reaction between diethyl thioxomalonate and derivatives of hexa-3,5-dienoic acid yields 5,6,6-trisubstituted 5,6-dihydro-2H-thiopyrans. The hydrolysis and decarboxylation of these compounds has been investigated. The iodo-lactonisation of these compounds has given a variety of products. Efficient routes have been developed to 4-formyl-3a,7a-dihydro-4H-thiopyrano[4,3-b]furan-2(3H)-one dimethyl acetal and the related malonic ester.