90862-65-0Relevant articles and documents
Electrocyclic Aromatic Substitution by the Diazo-group. Part 3. Studies on Substituent Directive Effects and on the Mechanism of Benzo-1,2-diazepine Formation by the Cyclisation of 1-Aryl-3-diazoalkenes
Miller, Thomas K.,Sharp, John T.,Sood, H. Raj,Stefaniuk, Edward
, p. 823 - 832 (2007/10/02)
The 1,7-cyclisation of diazo-compounds of type (4) which have an unsymmetrically placed substituent X gives both benzodiazepine isomers (6) and (8).The majority of substituents studied (X = R, OR, Cl) exert a directing effect which favours the formation of the less thermodynamically stable isomer (6) while only t-butyl and trifluoromethyl favour the formation of the para-isomer (8).A mechanistic study of the cyclisations of (6; X = Me and H) using 2H-labelled substrates has shown that the electrocyclisation step is reversible (Scheme 1 ; k-10).However for other substituents (X = OR, CF3, Cl) k-2(0)0 and the ortho-isomers undergo slow thermal isomerisation at 80 deg C to give the more stable para-isomers (8).The observed directing effects of the substituents X are exerted via their effects on k1, k-1, and k2 and although it is not possible to separate these effects for the majority of the substituents it was shown from the labelling study that the k2/k-1 ratio for the ortho-intermediate (5; X = Me) was markedly higher than that for the para-intermediate (7; X = Me).
