A General and Diastereoselective Approach to the Preparation of cis-2,6-Disubstituted Pyrans

Abstract

The utility of preparing cis-2,6-disubstituted 5,6-dihydro-2H-pyrans by the methodology implied in Scheme 1 is demonstrated through the preparation of the two pyrans (1) and (2). The overall yields for the two nine-step sequences starting from the enals (3) and (4) were 57 and 54%, respectively, whilst the overall diastereochemical yield approached 100%. The key features of the method are (i) a highly regioselective Lewis acid-catalysed cyclocondensation reaction of a nucleophilic diene with an aldehyde to afford a 2,3-dihydro-4H-pyran-4-one, (ii) reduction of a pyranone with better than 98% regio- and stereo-chemical control to give the corresponding glycal, and (iii) an ester enolate Claisen rearrangement of a glycal acetate.