A new fluorous soluble Lewis acidic borane system

Abstract

Treatment of trichlorovinylsilane with 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol (3 equiv.) in the presence of excess triethylamine produces the fluorous vinylsilane, 1, which can be isolated in 74% yield as an analytically pure oil. The addition of bis(pentafluorophenyl)borane to 1 produces the fluorous boranes, 2a–2b, as an analytically pure, isomeric mixture of anti-Markovnikov and Markovnikov hydroboration products in 38% isolated yield. Compounds 2a–2b are soluble in both arene solvents and perfluoro(methylcyclohexane). Treatment of 2a–2b with excess trimethylphosphine generates a mixture of products, including the Lewis adduct, 3, which can be isolated as an analytically pure oil in 15% yield. When exposed to either dimethylaminopyridine or piperidine at room temperature, the trimethylphosphine donor in 3 is cleanly displaced, based on in situ 31P NMR studies; under similar conditions, triethylamine does not react with 3. Addition of either dimethylaminopyridine or piperidine to 2a–2b, followed by purification and subsequent treatment with an excess of either hydrogen chloride or p-toluenesulfonic acid, results in cleavage of the Si–O linkages and the regeneration of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanol.Key words: fluorous, borane, silane, Lewis acid.

Phosphines and Related Tervalent Phosphorus Systems

“…The adduct is stable to trimethylamine. 512 Trimethylphosphine has also been shown to form P-B adducts with methyl(methylidene)boranes, MeB¼CR 2 . 513 Phosphine-borane adducts have been used as P-protecting systems in the synthesis of the chiral diphosphetanyl (176).…”