Haloaldehyde polymers, 43.. Structure of 2-bornyloxy-terminated chloral oligomers†
Haloaldehyde polymers, 43.. Structure of 2-bornyloxy-terminated chloral oligomers†
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卤醛聚合物，43.. 2-冰片氧基封端的三氯乙醛低聚物的结构†
DOI：
10.1002/macp.1991.021920104
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
O. Vogl
中科院分区：
文献类型：
--
作者：
K. Ute;K. Oka;M. Kashiyama;K. Hatada;F. Xi;O. Vogl
以（1 S，2 R，4S）-（-）-三氯乙醛锂盐为引发剂，进行三氯乙醛（三氯乙醛）的齐聚反应.单聚体和二聚体馏分分别由两种和四种非对映体组成;通过从甲醇中结晶或通过高效液相色谱法从馏分中分离出各个异构体。X-射线单晶分析表明，单聚体馏分中的主要异构体是（R）-型，其具有（R）-构型的缩醛碳。通过1H NMR测定非对映体比率，对于单聚体为R/S = 57/43，对于二聚体为RS/SR/RR/SS = 34/25/23/18。结晶形式的内消旋二聚体[（R，R）-和（S，S）-异构体]的构象对应于全同立构多氯醛的41-螺旋的半圈，而外消旋二聚体（（R，S）-和（S，R）-异构体）的构象不同于晶体和溶液中的螺旋结构。三聚体部分由八种可能的非对映异构体中的六种组成;在这些异构体中，mm异构体（（R，R，R）-和（S，S，S）-异构体）是高度主要的。形成的（R，R，R）-三聚体的量仅略大于（S，S，S）-异构体的量。(a)第42部分，参见G. D. Jaycox，O. Vogl，J. Am.化学会，已提交。
Oligomerization of trichloroacetaldehyde (chloral) was carried out with the lithium salt of (1 S, 2 R, 4 S)-(–)-borneol as the initiator. The unimer and dimer fractions consisted of two and four diastereomers, respectively; the individual isomers were isolated from the fractions by crystallization from methanol or by high performance liquid chromatography. The X-ray single-crystal analysis showed that the major isomer in the unimer fraction is the (R)-form which has the acetal carbon in (R)-configuration. The diastereomeric ratios were determined by 1H NMR as R/S = 57/43 for the unimers and RS/SR/RR/SS = 34/25/23/18 for the dimers. The conformations of the meso-dimers [(R,R)- and (S,S)-isomers] in the crystalline form corresponded to a half turn of the 41-helix of isotactic polychloral, whereas the conformations of the racemo-dimers (the (R,S)- and (S,R)-isomers) were different from the helical structure in the crystal and in solution. The trimer fraction consisted of six of the eight possible diastereomers; among these isomers, the mm isomers (the (R,R,R)- and (S,S,S)-isomers) were highly predominant. The amount of the (R,R,R)-trimer formed was only slightly larger than that of the (S,S,S)-isomer. (a) Part 42, cf. G. D. Jaycox, O. Vogl, J. Am. Chem. Soc., submitted.