Acceptorless, neat, ruthenium-catalyzed dehydrogenative cyclization of diols to lactones

We report the dehydrogenation of 1,4-butanediol to γ-butyrolactone catalyzed by soluble ruthenium complexes without solvent or a hydrogen acceptor. An alkylphosphine version of ruthenium bis-phosphine diamine catalysts has been prepared and was found to be the longest-lived catalyst for the conversion of 1,4-butanediol to γ-butyrolactone. The catalytic production of γ-butyrolactone from 1,4-butandiol with this catalyst is simple to conduct, environmentally friendly, and highly efficient.