Suppressing the Thermal Metacyclophanediene to Dihydropyrene Isomerization: Synthesis and Rearrangement of 8,16-Dicyano[2.2]metacyclophane-1,9-diene and Evidence Supporting the Proposed Biradicaloid M

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• 作者：Khurshid Ayub ; Rui Zhang ; Stephen G. Robinson ; Brendan Twamley ; Richard Vaughan Williams ; Reginald H. Mitchell
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：January 18, 2008
• 年：2008
• 卷：73
• 期：2
• 页码：451 - 456
• 全文大小：125K
• 年卷期：v.73,no.2(January 18, 2008)
• ISSN：1520-6904

文摘

Synthesis of 8,16-dicyano-anti-[2.2]metacyclophane-1,9-diene, 1b, was achieved in five steps from 1,3-bis(bromomethyl)benzonitrile. Unlike most metacyclophanedienes which easily thermally isomerize (_1/2= minutes to days at 20 C) to dihydropyrenes 2, dinitrile 1b shows no tendency to convert thermallyto 2b at room temperature (_1/2 > 30 years), consistent with predictions based on calculation of activationbarriers. Irradiation of cyclophanediene 1b with UV light readily forms the dinitriledihydropyrene 2b,which unexpectedly shows a much more facile (50 C) 1,5-sigmatropic rearrangement of the internalnitrile groups to give dihydropyrenes 9b and then 10b than is the case for internal methyl substituents,2a, which forms 9a at temperatures above 190 C. Synthesis of the 2-formyl derivative 1c and the2-naphthoyl derivative 1d are also described. These substituents were predicted to lower the activationbarrier for the thermal closing reaction to the corresponding dihydropyrenes, and experimental evidencesupports these calculations.