In:
Chemische Berichte, Wiley, Vol. 119, No. 2 ( 1986-02), p. 589-615
Abstract:
Photochemical Transformations, 64. The 3σ → 3π‐Route to Oxepines/Benzene Oxides The 7‐oxanorbornadiene skeleton ( 8a ), its 2,3‐bis(trifluoromethyl) derivative ( 8b ), and several 2,3‐dicarboxylic esters with potential dipolarophilic groups at C‐1 ( 16a – d, 17a – c ) were synthesized and selectively transformed into the 3‐oxaquadricyclanes ( 18a,b, 19a – d , and 20a – c ) through sensitized ( 8a,b ) or direct ( 16a – d, 17a – c ) photoexcitation. In the thermolysis of these oxaquadricyclanes [ 18a(b) : E a (C 6 D 6 ) = 32.6 ± 0.3 kcal/mol (32.2 ± 1.4 kcal/mol); lg A = 15.8 (14.5)] CF 3 (CH 3 CO 2 ) substituents at C‐2(3) favor the scission of the opposite (neighbouring) cyclopropane bonds. Competition experiments with dimethyl acetylenedicarboxylate as external dipolarophile support the stepwise mechanism of the oxaquadricyclane → oxepine conversion. The intramolecular carbonyl ylide‐interception cannot compete with oxepine formation in 19a – d but is efficient in 20a – c . The unusually low activation barrier ( E a (C 6 D 6 ) = 23.5 ± 1 kcal/mol; lg A = 11.6) and singular specifity in case of 20a is interpreted in terms of a concerted [ π 2 + σ 2 + σ 2]‐cycloaddition to the bishomofuran unit of the oxaquadricyclane skeleton.
Type of Medium:
Online Resource
ISSN:
0009-2940
DOI:
10.1002/cber.19861190222
Language:
English
Publisher:
Wiley
Publication Date:
1986
detail.hit.zdb_id:
1475009-0
