Studies on the Reaction of Aryl Glyoxals with l‐Prolinol: Unexpected Formation of Morpholin‐2‐one Derivatives and Stereoselective Trifluoromethylation of the Bicyclic System

Abstract

AbstractReactions of l‐prolinol with aryl glyoxals lead to labile bicyclic 2‐aryloyl‐1,3‐oxazolidines, which smoothly undergo isomerization in the presence of an acid via a cascade of reactions involving a 1,2‐aryl shift. The products formed thereby were identified as bicyclic derivatives of morpholin‐2‐one. Both 1,3‐oxazolidines and morpholin‐2‐ones were used for the nucleophilic trifluoromethylation by treatment with trifluoromethyltrimethylsilane (Ruppert–Prakash reagent) in the presence of a catalytic amount of CsF. Whereas in the case of the 1,3‐oxazolidines only modest diastereoselectivity was achieved, the reactions with the morpholinone derivatives occurred with complete stereoselectivity.