α,β-Unsaturated Carbonyls for One-Pot Transition-Metal-Free Access to 3,6-Dihydro-2H-pyrans

Abstract

An efficient protocol has been developed for accessing mono-, di-, and trisubstituted 3,6-dihydro-2H-pyran derivatives by simply subjecting α,β-unsaturated carbonyls to the carefully optimized Corey−Chaykovsky reaction conditions. The strategy provides selectively substituted dihydropyran derivatives in good to excellent yields with a broad substrate scope under very mild reaction conditions. Easy transformation of the final 3,6-dihydro-2H-pyran to the valued 5,6-dihydro-2H-pyran-2-one and tetrahydro-2H-pyran derivatives expanded the scope of this methodology to diverse oxacycles. Further, the developed strategy also found application in a two-step route to racemic goniothalamin, which is widely studied for its cytotoxic behavior.

(1RS,3SR)-1-(4-Methylbenzyl)-7-phenyl-5-oxa-6-azaspiro[2.4]hept-6-en-4-one

“…In our previous works, we have used different isoxazole derivatives as starting materials for the synthesis of nitrogen heterocycles [15][16][17][18]. In search of new isoxazole substrates, we became interested in isoxazol-5-ones spiro-fused with a cyclopropane ring.…”