Diastereoselective Synthesis of 2,6-Disubstituted Tetrahydropyranones via Prins Cyclization of 3-Bromobut-3-en-1-ols and Aldehydes

Tetrahydropyranones are synthesized from 3-bromobut-3-en-1-ols and aldehydes in good yields with excellent diastereoselectivity at -35 degrees C. The reaction involves an initial formation of a most stable six-membered chairlike tetrahydropyranyl carbocation followed by nucleophilic attack of the hydroxyl group and subsequent elimination of HBr to give tetrahydropyranone. The carbonyl moiety of the tetrahydropyranone is converted to enol ether and esters using Wittig reaction. It is also transformed into 4hydroxy-2,6-disubstituted tetrahydropyran with 2,4-and 4,6 -cis configuration by lithium aluminum hydride in up to 96% diastereoselectivity. Furthermore, the methodology is extended toward the synthesis of novel anticancer aminoguanidine compounds.