Organische Synthesen mit Übergangsmetall‐Komplexen, 60. Neuartige Benzoanellierung mit Carben‐Komplexen und Alkinen. – 2‐Oxybenzoanellierung von Cycloheptatrien über (Cycloheptatrienylmethyl)‐carben‐Komplexe von Chrom und Wolfram

Organic Syntheses via Transition Metal Complexes, 60. – Novel Type of Benzoanellation with Carbene Complexes and Alkynes. – 2‐Oxybenzoanellation of Cycloheptatriene via (Cycloheptatrienylmethyl)carbene Complexes of Chromium and Tungsten We report on a three‐step procedure for the regiospecific 2‐oxybenzoanellation to cycloheptatriene by means of Fischer carbene complexes and alkynes. The first step involves the formation of (cycloheptatrienylmethyl)carbene complexes L n MC(OEt)CH 2 ‐ c ‐C 7 H 7 [ 1 , L n M Cr(CO) 5 ( a ), W(CO) 5 ( b )] from the corresponding methylcarbene complexes and a tropylium salt. 1 reacts with the alkyne Et 2 NCCMe ( 2 ) to give the ( E )‐ and ( Z )‐1‐amino(1‐alkenyl)carbene complexes L n MC(NEt 2 )C(Me)C(OEt)CH 2 c ‐C 7 H 7 ( 3 and 4 resp.). Thermolysis of 3b [L n M = W(CO) 5 , 100°C, 5 h] finally leads to elimination of W(CO) 5 (Et 2 NH) ( 6b ) and the regiospecific formation of the ethoxybenzocycloheptatrienes 5,7 , and 8 in 92% total yield. The reaction is kinetically controlled and yields an isomeric ratio of 5:7:8 = 60:12:20% with the thermodynamically less stable isomer 5 predominating.