 These reactions employ electron-deficient sulfonyl azides, which undergo chemoselective, uncatalyzed [3+2] cycloaddition to the silyl enol ether, followed by loss of dinitrogen, and alkyl migration to give ring-contracted products in good yield.These reactions may be directed by substrate stereochemistry, giving rise to stereoselective ring-contracted product formation.Ketene silyl acetals are related compounds formally derived from ketenes and acetals with general structure R-C=C(OSiR3)(OR').