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For cyclohexenes carrying a hydroxy, methoxy, or ethoxy substituent (OR
group) without other steric hindrance, the ORgroup determines the
regiochemistry of the bromoalkoxylation with NBS in DMSO-H20 (95 : 5),
methanlo, or ethanol by the electronic effect, and in the mean time, by
the steric hindrance from these groups, directs the course of the reaction
and the steroechemistry of the product. The reaction is highly
regioselective and stereoselective. When the size of the OR group or
electrophile increased, the stereoselectivity of the reaction decreased.
However, the size of the nucleophile does not significantly affect the
stereoselectivity of the reaction. Therefore, by choosing the suitable OR
group and electrophile, the course of the reaction could be effectively
controlled, and the stereoselectivity of the reaction can be manipulated.
The reaction pathway and mechanism are also discussed.
具羥基，甲氧基，或乙氧基（統稱OR基）取代的環己烯類以 NBS在CMSO- 水（95：5
），甲醇，或乙醇中進行溴烷氧基化反應時，若結構中無其它立體障礙存在，OR基以
其電子效應決定反應之位置化學，同時，由OR基而來的立體障礙會導引反應之過程而
決定產物的立體化學，使反應具高位置選擇性及高立體選擇性。若將OR基或親電性基
變大反應之立體選擇性會降低。然而改變親核性基對反應之立體選擇性並無顯著的影
響。故只要選擇適當的OR基及親電性基，即可有效率地控制反應之進行過程而得到高
立體選擇性的產物。關於反應進行之途徑及機轉本文也有詳細的討論。
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