The question of exo vs endo cyclisation. A joint experimental and ab initio study on the stereoselective synthesis of tetrahydrofurans and tetrahydropyrans via seleniranium ions
The question of exo vs endo cyclisation. A joint experimental and ab initio study on the stereoselective synthesis of tetrahydrofurans and tetrahydropyrans via seleniranium ions
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DOI：
10.1016/s0040-4020(00)01154-6
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发表时间：
2001-02-25
期刊：
影响因子：
2.1
通讯作者：
Noto, R
中科院分区：
文献类型：
--
作者：
Gruttadauria, M;Lo Meo, P;Noto, R
研究了羟基硒醚与催化量高氯酸在二氯甲烷中的反应性。中间体硒铱离子可发生4-exo、5-endo、5-exo和6-endo四种不同的环化模式。羟基硒化物与相同侧链中的伯羟基和仲羟基的反应首先导致来自5-外环化的四氢呋喃的混合物（动力学产物），然后导致来自6-内环化的四氢吡喃的68/32混合物（热力学产物），可能通过两个非对映体硒杂环离子。实验和从头算（HF/3- 21 G *）研究表明，中间体硒氮杂环离子的环化反应级数为5-exo-tet
The reactivity of hydroxy selenides with catalytic amounts of perchloric acid in dichloromethane was investigated. Four different cyclisation modes (4-exo, 5-endo, 5-exo and 6-endo) of the intermediate seleniranium ion could occur. The reaction of the hydroxy selenides with primary and secondary hydroxyl groups in the same side chain led first to a mixture of tetrahydrofurans from the 5-exo cyclisation (kinetic products), then to a 68/32 mixture of tetrahydropyrans from the 6-endo cyclisation (thermodynamic products) probably via two diasteromeric seleniranium ions. Both experimental and ab initio (HF/3-21G*) studies showed that the order of cyclisation of the intermediate seleniranium ion was 5-exo-tet