Uncovering Reaction Pathways of 1‐Aminocyclohexenes with [(1‐Alkynyl)carbene]tungsten Complexes Leading to Cyclopentadienes and Dihydropyrroles

Reactions of the [(1‐alkynyl)carbene]tungsten complex (CO) 5 WC(OEt)C≡CPh ( 1 ) with 1‐aminocyclohexenes 2a ‐ c and 7a ‐ c afford different types of products depending on the amino substituents and the reaction conditions. (4‐Aminocyclobutenyl)carbene complexes B have been shown to be generated in the first reaction step through a [2+2] cycloaddition. These are key intermediates and afford cross‐conjugated tungstatrienes E , (conjugated) 1‐tungsta‐1,3,5‐hexatrienes G , or (non‐conjugated) 1‐tungsta‐1,3,6‐heptatrienes F by following competing reaction pathways. Cross‐conjugated 1‐tungstatrienes 3 have been isolated in 52‐74% yield by performing the reactions of 1‐aminobenzocyclohexenes 2a ‐ c with compound 1 in pentane. In dichloromethane instead of pentane, (conjugated) 1‐tungsta‐1,3,5‐hexatrienes 4 are obtained, which subse‐quently undergo fragmentation to give cyclopentadienes 6 (by π‐cyclization) and dihydropyrroles (by α‐cyclization) in a molar ratio dependent on the nature of the amino substituents. (Non‐conjugated) 1‐tungsta‐1,3,6‐heptatrienes 10 are generated upon reaction of 1‐aminocyclohexenes 7a ‐ c with compounds 1 , which are transformed into cyclopentadienes 12 via conjugated 1‐tungsta‐1,3,5‐hexatrienes 9 as intermediates. Reactions of 1‐tungsta‐1,3,6‐heptatrienes 10 with the (1‐alkynyl)carbene complex 1 afford dinuclear compounds 14 , which subsequently yield indenes 15 (by two successive π‐cyclization steps) and spiro ‐tetrahydropyrroles 16 (by both a π‐cyclization and an α‐cyclization step), depending on the steric bulk of the amino substituent.