Novel Intramolecular Cyclization of 2-(Buta-1,3-dienyl)benzyl Anions to 6,7(9)-Dihydro-5H-benzocycloheptenyl Anions Leading to Successive Formation of 1,2-Dihydrocyclopropa[a]naphthalenes

When treated with LiNiPr2 (LDA) at −78°, 1‐[(methylsulfanyl)methyl]‐2‐[(1Z,3E)‐4‐phenylbuta‐1,3‐dien‐1‐yl]benzene easily cyclized to form benzocycloheptenyl anion, which successively underwent intramolecular nucleophilic substitution to give a cyclopropanaphthalene. Similar LDA‐mediated cyclization also occurred for 4‐phenyl‐ or 4‐methyl‐substituted 1‐[2‐(methoxymethyl)phenyl]buta‐1,3‐dienes to furnish the corresponding benzocycloheptenes and cyclopropanaphthalenes. A 4‐tert‐butyl analog also underwent LDA‐mediated cyclization to give a benzocycloheptene, but not a cyclopropanaphthalene.