In:
Chemische Berichte, Wiley, Vol. 119, No. 2 ( 1986-02), p. 616-644
Abstract:
Photochemical Transformations, 65. The 3σ → 3π‐Route to 1 H ‐Azepines/Benzene Imines With several newly prepared substrates the influence of substituents upon the individual steps in the 3σ → 3π‐route to 1 H ‐azepines is more precisely defined: The C ‐unsubstituted 7‐azanorbornadiene 2a , its 2,3‐dichloro derivative 2b , the dimethyl 5,6‐dichloro‐2,3‐dicarboxylate 2c , and the diesters 2d,e with dipolarophilic groups at C‐1/N‐7 are selectively isomerized by sensitized/direct photoexcitation into the azaquadricyclanes 29a – e , some of which are highly unstable. For the thermal conversion of the basic skeleton ( N ‐Tos) 29a the kinetic parameters have been determined (benzene): E a = 28.0 ± 0.2 kcal/mol, lg A = 15.7; Δ H ≠ = 27.3 ± 0.2 kcal/mol, Δ S ≠ = 11.1 ± 0.7 e.u. This barrier is lowered more efficiently by the chloro ( 29b,c ) than by the methoxycarbonyl substituents ( 29f ), with the former (latter) causing exclusive scission of the opposite (neighbouring) cyclopropane bonds. The intermediate azomethine ylides are captured with dipolarophilic reagents more or less efficiently depending on their substitution pattern. In the case of 29d(28d) the intramolecular addition of the unactivated yne component ( 37 ) at −30°C is so fast, that azepine formation is almost totally suppressed ([ π 2 + σ 2 + σ 2], 36 ?). The azepine/benzene imine equilibrium mixture 31c⇄32c (ca. 90:10) crystallizes as 31c ( X ‐ray crystal structure analysis).
Type of Medium:
Online Resource
ISSN:
0009-2940
DOI:
10.1002/cber.19861190223
Language:
English
Publisher:
Wiley
Publication Date:
1986
detail.hit.zdb_id:
1475009-0
