cis-Oxa,aza-σ-homobenzenes : Syntheses,[2+2+2]-cycloreversion reactions

Abstract cis -Dioxa,aza-tris-(8) and cis -oxa, aza-bis-σ-homobenzenes (21) have been synthesised. With activation barriers, which clearly support the concerted mechanism, they undergo [2+2+2]-cycloreversion yielding 7H-1,4,7-dioxazonines (9) and 4H-1,4-oxazocines (22), resp.