Stereochemical Studies of Thermal Intermolecular and Intramolecular N-Sulfonylimine Ene Reactions

N-Sulfonylimine 2 has been found to undergo highly stereoselective thermal ene reactions with cyclohexene and trans-2-butene. In the cyclohexene example, the exclusive product was unsaturated amino acid derivative 6, the product of an endo transition state. With trans-2-butene, a 9:1 mixture of 18:22 was obtained, with the endo product again predominating. Intramolecular ene processes have been effected with the N-sulfonylimines derived from glyoxylates 25c and 26c. In the former case, the sole ene product was γ-lactone 30 derived from exo addition. In the latter process, a 9:1 mixture of cis-(E)-lactone 32 and cw-(Z)-lactone 33 was produced. Lactone 32 results from endo ene transition state 35 and 33 results from endo transition state 36. All attempts to effect intermolecular ene reactions of N-benzoylimine 39 failed. In trying to perform an intramolecular N-acylimine ene reaction, only Diels-Alder adduct 45 was produced from precursor 42.