Allenyl Azide Cycloaddition Chemistry: Exploration of the Scope and Mechanism of Cyclopentennelated Dihydropyrrole Synthesis through Azatrimethylenemethane Intermediates

Abstract

Detailed studies of the thermal conversion of 1-azidohepta-3,4,6-trienes into cyclopentennelated dihydropyrroles are presented. High levels of diastereoselectivity and regioselectivity are documented. A mechanistic proposal that accounts for all of the diverse results is developed through the use of density functional calculations. These calculations provide support for the intervention of unexpected mechanistic subtleties, such as the planarity of an azatrimethylenemethane diyl intermediate and an apparent Woodward-Hoffmann-type electrocyclization of a five-atom diyl array.

Cyclization Cascade of Allenyl Azides: Synergy Between Theory and Experiment

“…8) [18]. Both allenyl azide derivatives afforded the expected products (after imine capture with TMS-CN) in moderate yields.…”

Carbon–Carbon Bond Forming Reactions Mediated by Organozinc Reagents

“…1,4-Dienes are formed in excellent yields and stereochemical purity (Scheme 4.52). In contrast, the related reaction of alkenylzincs with propargylic mesylates catalyzed by Pd(PPh 3 ) 4 occurs γ-selectively and provides the corresponding allenenes [191]. Scheme 4.52 α-Selective Pd-catalyzed cross-coupling of alkenylzinc reagents with allylic halides [190].…”

Reaction mechanisms : Part (ii) Pericyclic reactions

“…Feldman, Lo´pez and co-workers described an experimental/computational (B3LYP/6-311+G(d,p)//B3LYP/6-31G(d,p)) study on the mechanism of the tandem cycloaddition/cycloreversion/electrocyclization cascades shown in Scheme 60. 67 Biradical intermediates were proposed and the regio-and stereoselectivity of these cascades were ascribed to spin density distributions in the intermediates, and to orbital symmetry control, respectively. Domingo and co-workers utilized B3LYP/6-31G* calculations to characterize the mechanism of the tandem cycloaddition/HNO 2 extrusion reactions shown in Scheme 61.…”