Synthesis of α-Cyano and α-Sulfonyl Cyclic Ethers via Intramolecular Reactions of Peroxides with Sulfone- and Nitrile-Stabilized Carbanions

Abstract

The intramolecular reaction of carbon nucleophiles with oxygen-centered electrophiles has been little explored outside of nucleophilic epoxidation. We now report the synthesis of sulfonyl- and cyano-substituted oxacycles via intramolecular reaction of sulfone- and nitrile-stabilized carbanions with dialkyl peroxides, triethylsilyl/alkyl peroxides, and monoperoxyacetals. The cyclizations are successfully applied to synthesize oxetanes, tetrahydrofurans, and tetrahydropyrans but fail for oxepanes. Cyclizations involving the relatively stabilized anion derived from a benzylic nitrile proceed in high yields for a variety of peroxides, including those in which the electrophilic oxygen is formally isobutyl or neopentyl. Corresponding cyclizations of an alkanenitrile are successful with both dialkyl and alkyl silyl peroxides but demonstrate much greater variability in yields. Reactions of sulfone-containing substrates are successful only with dialkyl peroxides. The success of reactions appears to be strongly influenced by the rate of peroxide decomposition, which appears to be highest for reactions involving poorly stabilized anions. The significant variation in diastereoselectivity observed for different classes of peroxide on a common framework suggests the possibility of substrate-dependent reaction mechanisms.