Competitive reactions between sigmatropic reaction and cycloaddition affected by geometry of o-quinodimethanes

Abstract

This paper describes a new type of reaction, [1,5]-sigmatropic hydrogen migration, of benzocyclobutenes, and also reports a direction of ring opening of benzocyclobutenes and a geometry of o-quinodimethanes.Benzocyclobutenes (l)1 are one kind of charming and effective intermediates for a construction of the natural prod-

Approach to a New Dihydrofuran‐Fused Cyclic System by a Remarkable Switching of endo/exo Selectivity of a [4+2] Cyclo­addition Reaction

“…The ring-opened olefin product 16 may be formed by [1,5] sigmatropic rearrangement of the o-quinodimethane intermediate (probably a geometric isomer of 10), as previously discussed. [10] Furthermore, 14b was synthesized in a higher yield than 14a. Although the two isomers of 14b, as well as those of 14a, were inseparable at this stage, chromatographic separation was achieved after desi-lylation by treatment with TBAF.…”

Application ofo-Quinodimethanes in Organic Synthesis

“…对高张力的苯并环丁烯衍生物 5 进行热解开环是产 生 o-QDM 衍生物最常见的方法 [1,2] . 如 Scheme 6 所示, 反应一般优先生成空间位阻较小的 E-二烯烃 [13] , 同时, 开环的难易程度也受到四元环上取代基性质的影响 [14] . 当取代基 R 为氨基(R＝NH 2 )时, 开环所需温度只需要 25 ℃, 而当取代基为羟基(R＝OH)时开环温度需要 80 ℃, 而当取代基为酰胺(R＝NHCOR')或烷基(R＝Alkyl) 时, 开环温度分别为 110 和 180 ℃ [13] .…”

Cycloadditions in syntheses. XXXV. 2-Cyano-1,2-dihydrocyclobuta[a]naphthalene and its derivatives: synthesis and reaction with olefins.

“…Thus, in order to synthesize these acids (F: Y =CO2H), use of the ester (6) instead of 3 as the starting material in the above transformation was examined. When 6 was treated with 5-bromo-1 -pentene under the same conditions as in the case of 3 until disappearance of the starting material , several compounds (15, 16, and 17) were obtained, together with a small amount (7%) of the simple hydrolysis product (5). It was found, however, that further exposure of this product mixture to the same conditions resulted in exclusive formation of 17 , with the consumption of both 15 and 16.…”