Reactant for: (1) preparation of unsaturated hydroxymethylene diphosphonic acid derivatives by reaction of trimethylsilyl phosphites, (2) asymmetrical synthesis of the isoindolinone subunit of the macrocyclic poylketide natural product muironolide via stereoselective intramolecular Diels-Alder cycloaddition, (3) preparation of emollient, humectant, and fluorescent alpha,beta-unsaturated thiol esters for long-acting skin applications, (4) stereoselective synthesis of enediol carbonates for use in the asymmetrical synthesis of alpha-acyloxyketones, (5) acylation of pyrazoles.