Organotin-mediated monoacylation of diols with reversed chemoselectivity: a convenient synthetic method

The organotin-mediated monoesterification of unsymmetrical diols with reversed chemoselectivity has been explored to ascertain scope and limits of the method and to provide an easy and convenient synthetic procedure. The reaction has been performed on a set of substituted diols with some acylating agents usually employed as protecting groups. Two different procedures have been devised to obtain either the desired diol monoesters directly or the corresponding trialkylsilyl ethers as protected derivatives. The latter provides a convenient approach to the preparation of easily interconvertible diol monoesters. Also, the reaction has been optimized as a one-pot procedure, avoiding the isolation and purification of the stannylated intermediates. The reversed monoesterification method has been successfully applied to 1,2-, 1,3-, and 1,4-diols of primary-secondary, primary-tertiary, and secondary-tertiary types and to ether functions containing 1,2-diols. Within its limits, the described method represents the first direct one-pot monoesterification of diols at the most substituted site, allowing some remarkable achievements as (a) an almost regiospecific reversed monobenzoylation of some l,e-diols, (b) the selective acylation of the tertiary hydroxyl of a primary-tertiary diol, and (c) a highly selective preparation of the secondary pivalate of primary-secondary diols