Cycloaddition of nitrones to 1,3-diarylpropenones and subsequent transformations of the resulting isoxazolidines

Ketonitrones containing two ester groups react regio- and stereoselectively with 1,3-diarylpropenones to form isoxazolidines with ester groups at position 3 of the ring. The action of zinc in acetic acid on these isoxazolidines causes opening of the ring with the formation of 3-amino alcohols, the subsequent cyclization of which leads to polysubstituted lactones. Reduction of the benzoyl group of isoxazolidine with sodium borohydride leads, as a result of subsequent transformations, to the formation of substituted 1,3,4-triaryl-6-oxodihydro-1 H ,3 H -furo[3,4- c ]isoxazole-6a(6 H )-carboxylates as single diastereomers.