Directed Ring-Opening of 1,5-Dioxaspiro[3.2]hexanes: Selective Formation of 2,2-Disubstituted Oxetanes

Abstract

1,5-Dioxaspiro[3.2]hexanes undergo ring-opening reactions with many heteroatom nucleophiles to provide α-substituted-β‘-hydroxy ketones. However, certain Lewis acidic nucleophiles provide 2,2-disubstituted oxetanes. Herein, the results of reactions of 3-phenyl-1,5-dioxaspiro[3.2]hexane with a variety of nitrogen-containing heteroaromatic bases are reported. There appears to be a correlation between the pKa of the nucleophile and the reaction outcome with more acidic nucleophiles providing 2,2-disubstituted oxetanes. Moreover, the mode of ring opening can be directed toward the substituted oxetane by the addition of a Lewis acid. These results are rationalized by calculation of stationary points on the potential energy surfaces for the various possible reaction pathways using ab initio molecular orbital methods.