Synthesis and Cleavage of the Cyclic Oxalates of 1,2-Glycols.

我们已经公开了草酰氯与无环1，2-二醇在四氢呋喃中在三乙胺存在下反应，得到不同类型的化合物作为主要产物，这取决于二醇的结构：未取代的、单取代的和赤型-二取代的乙二醇提供环状碳酸酯或聚合碳酸酯，而苏式异构体和频哪醇得到环状碳酸酯。1.我们发现的唯一例外是反式环己烷-1，2-二醇，它专门得到环状碳酸酯。该反应可能是通过船形四面体中间体进行的，避免了桥头氢和羰基氧之间的空间干扰。2.在与频哪醇或苏式化合物的反应中，用吡啶代替三乙胺，实现了产物比的急剧逆转，得到了环状的双酯。发现1，1 '-草酰二咪唑是一个很好的选择，为独家形成的环状双酯。2，4，6-可力丁完全抑制了赤式化合物形成聚合草酸酯的反应。3.所得环状草酸酯在pH 5时发生酰基-烷氧基键水解断裂，生成草酸单酯，其水解速度比环状草酸频哪醇快200-1000倍。通过X-射线晶体分析阐明的三维结构表明，频哪醇的环状草酸酯的羰基碳被四个甲基中的两个有效地阻断。

We have already disclosed that oxalyl chloride reacts with acyclic 1,2-glycols in tetrahydrofuran in the presence of triethylamine to afford a different type of compound as a major product, depending on the structure of the glycol : unsubstituted, monosubstituted, and erythro-disubstituted ethylene glycols provided the cyclic oxalates or polymeric oxalates, while the threoisomers and pinacol afforded the cyclic carbonates.1.The only exception we found was trans-cyclohexane-1,2-diol, which exclusively afforded the cyclic oxalates. This reaction probably proceeded through the tetrahedral intermediate with a boat form, avoiding steric interference between the bridge-head hydrogen and carbonyl oxygen.2.The dramatic reversal of the product ratio was realized in the reaction with pinacol or the threo-compounds by the use of pyridine instead of triethylamine to afford the cyclic oxalates. 1,1'-Oxalyldiimidazole was found to be a good choice for the exclusive formation of the cyclic oxalates. The formation of the polymeric oxalates from the erythro-compounds was completely suppressed by the use of 2,4,6-collidine.3.The cyclic oxalates thus obtained underwent hydrolytic cleavage of the acyl-alkoxy linkage to afford the monoester of oxalic acid at pH 5 at the rate of 200-1000 times faster than the cyclic oxalate of pinacol. The three-dimensional structure elucidated by X-ray crystal analysis shows that the carbonyl carbons of the cyclic oxalate of pinacol are effectively blocked by two of the four methyl groups.