Abstract
Treatment of tungsten-η 1 -αδ-alkynylamine compounds with aldehyde and BF 3 Et 2 O led to cycloalkenation reaction, giving good yields of tungsten- η 1 -pyrrolylidium salts. These azacyclic carbeniums provide a short synthesis of α-alkylidene-γ-lactam via oxidation with m-CPBA. In contrast with tungsten-η 1 -oxacyclic carbenium, this salt reacts with one molecule of organometallic reagents such as NaBH 3 CN, CH 3 MgBr and Me 2 CuLi to give tungsten-η 1 -4,5-dihydropyrrole complexes. An alternative use of this cyclialkenation is to provide a short synthesis of 3-vinyl-Δ 2 -pyrrolines. (C) 2000 Elsevier Science Ltd. All rights reserved.