SELECTIVE CATALYTIC TRANSESTERIFICATION, TRANSTHIOLESTERIFICATION, AND PROTECTION OF CARBONYL-COMPOUNDS OVER NATURAL KAOLINITIC CLAY

Transesterification and transthiolesterification of beta-keto esters w ith variety of alcohols and thiols and selective protection of carbony l functions with various protecting groups catalyzed by natural kaolin itic clay are described. The clay has been found to be an efficient ca talyst in transesterifying long chain alcohols, unsaturated alcohols, and phenols to give their corresponding beta-keto eaters in high yield s. For the first time, transthiolesterification of beta-keto eaters wi th a variety of thiols has been achieved under catalytic conditions. C lay also catalyzes selective transesterification of beta-keto eaters b y primary alcohols in the presence of secondary and tertiary alcohols giving corresponding beta-keto esters. A systematic study involving th e reactivity of different nucleophiles (alcohols, amines, and thiols) toward beta-keto esters is also described. Sterically hindered carbony l groups as well as alpha,beta-unsaturated carbonyl groups underwent p rotection without the deconjugation of the double bond. Chemoselective protection of aldehydes in the presence of ketones has also been achi eved over natural kaolinitic clay.