Molecular addition compounds. 18. Borane adducts with hydroxydialkyl sulfide borates for hydroboration. New, essentially odorless, water-soluble sulfide borane acceptors for hydroboration.
Hydroxydialkyl sulfides of general formula RS(CH2CH2)nH (R = Et, t-Bu, i-Am; n = 1-3) and thiodiethanol monomethyl ether (9) have been synthesized and used as borane carriers. The compounds 3 and 6 (R = Et, n = 2, 3), 7 (R = t-Bu, n = 3), and 9 are completely miscible with water and exhibit only very mild odor. The sulfides were transformed into the corresponding borates by treatment either with boric acid or with diborane. The borates complex 3 mol of borane per 1 mol of borate to give highly reactive, stable, liquid adducts, hydroborating 1-octene in 15 min at room temperature. The adducts derived from water soluble sulfides 3 and 9, selected for the hydroboration of more hindered olefins, reacted readily with (-)-beta-pinene, 1-methylcyclohexene, and 2,3-dimethyl-2-butene. The carrier borates liberated from the adducts during hydroboration are readily hydrolyzed to give 3 and 9, which can be washed off with water from trialkylboranes or oxidation products. Consequently, hydroxydialkyl sulfides 3 and 9 are the first completely water-soluble sulfide borane carriers that can be washed off in the workup of hydroboration products. The adducts derived from 3 and 9 are new, highly promising reagents suitable for large scale hydroborations and reductions.
Brown
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H. C. Brown Center for Borane Research, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA. hcbrown@purdue.edu
Zaidlewicz
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Dalvi
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Biswas
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