Steric Effects in the Cycloaddition of Electron-Deficient 8,8-bis(Methoxycarbonyl)heptafulvene to Electron-Rich Unsymmetrically 6-Methyl-6-phenylfulvene

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Title:	Steric Effects in the Cycloaddition of Electron-Deficient 8,8-bis(Methoxycarbonyl)heptafulvene to Electron-Rich Unsymmetrically 6-Methyl-6-phenylfulvene 缺電子基取代之8,8-bis(Methoxycarbonyl) heptafulvene和給電子基不對稱取代之6-Methyl-6-phenylfulvene的還化加成反應研究探討: 立體效應影響性
Authors:	劉清揚陳信尹
Contributors:	化學系
Date:	1993-05
Issue Date:	2016-04-13 14:22:14 (UTC+8)
Abstract:	缺電子基取代之8，8-bis（methoxycarbonyl）heptafulvene（2）和給電子基不對稱取代之6-methyl-6-phenylfulvene（5）進行還化加成反應研究探討。由實驗結果顯示，溫度效應為控制其還化加成反應之重要因素．Heptafulvene2只會和fulvene5進行[8+2]還化加成反應，且意外地只得到[8+2]"順式"加成生成物6和7。在所有進行的反應當中，並未有分離出任何的[4+2],[6+4]與（anti）[8+6]還化加成生成物。其進行還化加成反應只顯示出的“反向”位向選擇性（regioselec-tivity），可以歸因於heptafulvene2和fulvene5的環外取代基（exosubstituents）相互之間巨大排斥力所至。 Thermal cycloaddition reaction of electron-deficient 8,8-bis (methoxycarbonyl) heptafulvene (2) with electron-rich unsymmetrically 6,6-disubstituted6-methyl-6-phenylfulvene (5) was examined to determine the effects ofthe fulvene exocyclic substituents on this cycloaddition. 2 eacted with 5 to afford only the unexpected [8+2] adducts6 and 7,both with the methylgroup cis to H-6. In no caseswere [4+2], [6+4]and [8+6]cycloadducts obtained. The reaction shows a temperature dependency. The exclusively anti regioselectivity can be attributed tothe enormoussteric repulsion between the exocyclic substituents on theheptafulvene andfulvene.
Relation:	華岡理科學報 10 民82.05 頁85-92
Appears in Collections:	[Department of Chemistry & Graduate Institute of Applied Chemistry ] journal articles

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