A Novel and Mild Procedure for Preparation of Cyclic Carbonates. An Excellent Protecting Group for Vicinal Diols

Abstract

In a synthetic problem in our laboratory it became necessary to provide a protecting group for a vici-nol diol which, due to the functionality elsewhere in the molecule, could be subsequently removed under very mild conditions. From these and other considerations, the cyclic carbonate group was selected as perhaps being the most suitable. This protecting group is well known and its use, particularly in the carbohydrate area, is well documented in the literature^2–4. The usual procedure employing phosgene or alkyl chloroformates proved undesirable. For example, the diol, desacetylvindoline (I) provided essentially no cyclic carbonate when reacted with ethyl chloroformate even under forcing conditions. In search for a solution to this problem, we have found that N,N′-carbonyldiimidazole is an excellent reagent for this purpose and provides the cyclic carbonates in very high yields. The reagent is easily available by synthesis ^5,6 or commercially⁷ and apart from the high yields obtained, the procedure is so straightforward that it undoubtedly provides the method of choice f o r preparation of cyclic carbonates. Imidazole as the only other product formed is easily removed from the desired material.