ISSN:
0009-2940
Keywords:
Carbene complexes, cycloaddition reactions of
;
Carbene complexes, reactions with alkynes
;
Benzocyclo-heptatrienes
;
2-Oxybenzoanellation
;
(Cycloheptatrienylmethyl)carbene complexes of chromium and tungsten
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 TungstenWe 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 LnM=C(OEt)—CH2-c-C7H7 [1, LnM = Cr(CO)5 (a), W(CO)5 (b)] from the corresponding methylcarbene complexes and a tropylium salt. 1 reacts with the alkyne Et2N—C≡C—Me (2) to give the (E)- and (Z)-1-amino(1-alkenyl)carbene complexes LnM=C(NEt2)—C(Me)=C(OEt)—CH2—c-C7H7 (3 and 4 resp.). Thermolysis of 3b [LnM = W(CO)5, 100°C, 5 h] finally leads to elimination of W(CO)5(Et2NH) (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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19921250812
