[3+2] Cycloaddition of trimethylenemethane (TMM) to α,β-unsaturated γ-lactam. Preparation of 5,5-fused proline surrogates

Unsaturated lactam derived from (S)-pyroglutaminol undergoes a totally stereoselective cycloaddition reaction with (2-(acetoxymethyl)-3-allyl)trimethylsilane in the presence of Pd(P(OiPr)3)4 in refluxing toluene. This step was efficiently used to introduced the 5,5-fused framework desired for the preparation of novel proline surrogates.