Elemination Reactions of α-Halogenated Ketones. XII.1aCarbon-Halogen and Carbon-Hydrogen Bond Strengths as Orientation and Rate-Determining Factors. Deuterium Isotope Effects in Dehydrobromination of 2-Bromo-2-benzyl-1-indanone1b
Elemination Reactions of α-Halogenated Ketones. XII.1aCarbon-Halogen and Carbon-Hydrogen Bond Strengths as Orientation and Rate-Determining Factors. Deuterium Isotope Effects in Dehydrobromination of 2-Bromo-2-benzyl-1-indanone1b
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α-卤代酮的元素化反应。
DOI：
10.1021/ja01062a020
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发表时间：
1964
影响因子：
15
通讯作者：
N. Cromwell
中科院分区：
文献类型：
--
作者：
D. N. Kevill;G. Coppens;N. Cromwell
研究发现，在卤离子促进的卤代四氢萘酮和茚满酮的消除反应中，碳-卤键的强度是一个极其重要的速率决定因素。氘取代2-溴-2-苄基-1-茚满酮（IV）的外苄基亚甲基质子导致低氘同位素效应，这与具有碳-卤素键断裂在碳-氢键断裂之前充分进行的速率决定步骤的过渡态一致。哌啶攻击2-溴-2-（α，β-二氘代苄基）-1-茚满酮（IVa）导致通过内环脱溴化氢随后1，4-加成形成的3-哌啶子基-2-（α，β-二氘代苄基）-1-茚满酮（Via）的大量产率。环外氘取代导致了反应途径的显著变化，并提示了氘取代在其它精细平衡体系中控制消除方向的可能性。
It has been found that, in halide ion promoted elimination from-halogenated tetralones and indanones, the strength of the carbon-halogen bond is an extremely important rate-determining factor. Deuterium sub-stitution for the exo-benzylic methylene protons of 2-bromo-2-benzyl-1-indanone (IV) leads to a low deuterium isotope effect, consistent with the transition state of the rate-determining step having carbon-halogen bond breaking running well ahead of carbon-hydrogen bond breaking. Attack of piperidine upon 2-bromo-2-(a, adideuteriobenzyl)-1-indanone (IVa) leads to substantial yields of 3-piperidino-2-(a,-dideuteriobenzyl)-1-indan-one (Via) formed by an endocyclic dehydrobromination followed by a 1, 4-addition. The exocyclic deuterium substitution leads to a marked change in the reaction pathway andsuggests the possible use of deuterium substitution for controlling the orientation of elimination in other delicately balanced systems.