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Alkylphenyl sulfones 3 are appropriate synthons for the synthesis of 2-phenylsulfonyl alkylidene pyrrolidine or piperidine derivatives 1 in good to moderate yields. The lithium alkyl sulfones 4 are first reacted with the desired protected lactams and then subjected to acidic methanolysis to afford the unusual enamines 1a-e. NMR studies (COSY 1 H-1 H, COSY 1 H-13 C, NOE) showed the Z enamines to exist in a dynamic equilibrium with the corresponding imines 2. The stereochemistry of the described compounds was confirmed by molecular calculations.

The low temperature addition of dilithiomethylphenyl sulfone to 2,3‐O‐isopropylidene‐D‐erythronolactone, and to 5‐O‐(tert‐butyldimethylsilyl)‐2,3‐O‐isopropylidene‐D‐ribofuranolactone gives the lactols 2 and 3a, respectively. Dehydration of lactol 2 in the presence of boron trifluoride etherate produces tetrahydrofuranylidene sulfones 5 and 6 in good yields. The reaction of lactol 3a under the same reaction conditions proceeds with formation of the 1′,5′‐anhydro derivative 7 via competing intramolecular substitution.