Efficient synthesis of new phosphono-substituted dihydrothiopyrans via hetero Diels-Alder reaction, under thermal and high pressure conditions

New alpha-phosphono-beta-aryl- or beta-heteroaryl-substituted alpha,beta-un saturated dithioesters 2 were easily prepared from diethyl phosphonodithioa cetate 1 and used as thiadienes in thermal or high pressure hetero Diels-Al der cycloadditions with enol and thioenol ethers. The resulting new phospho no 3,4-dihydro 2H-thiopyrans 3 were isolated in excellent yields and with a cis- or trans-diastereoselectivity depending on the conditions of the reac tion as well as the structure of the reagents. Some of the thiopyrans 3 wer e also favourably synthesized via a domino Knoevenagel-hetero Diels-Alder s equence. (C) 2000 Elsevier Science Ltd. All rights reserved.