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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Dowd–Beckwith ring-expansion reaction ： ウィキペディア英語版 Dowd–Beckwith ring-expansion reaction The Dowd–Beckwith ring-expansion reaction is an organic reaction in which a cyclic β-keto ester is expanded by up to 4 carbons in a free radical ring expansion reaction through an α-alkylhalo substituent . The radical initiator system is based on AIBN and tributyltin hydride. The cyclic β-keto ester can be obtained through a Dieckmann condensation. The original reaction consisted of a nucleophilic aliphatic substitution of the enolate of ethyl cyclohexanone-2-carboxylate with 1,4-diiodobutane and sodium hydride followed by ring expansion to ethyl cyclodecanone-6-carboxylate. A side-reaction is organic reduction of the iodoalkane. == Reaction mechanism== The reaction mechanism involves a bicyclic intermediate. The reaction is initiated by thermal decomposition of AIBN. The resulting radicals abstract hydrogen from tributyltin hydride to a tributyltin radical which in turn abstracts the halogen atom to form an alkyl radical. This radical attacks the carbonyl group to an intermediate bicyclic ketyl. This intermediate then rearranges with ring expansion to a new carbon radical species which recombines with a proton radical from tributyltin hydride propagating the catalytic cycle. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dowd–Beckwith ring-expansion reaction」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.