Morris Srebnik

Chiral Oxazaborolidines as Catalysts for the Enantioselective Addition of Diethylzinc to Aldehydes

(4S, 5R)-3,4-dimethyl-5-phenyl-1,3,2-oxazaborolidine, 1, catalyzes the addition of diethylzinc to aldehydes to furnish secondary alcohols in up to 96% ee. This is the first example of a chiral boron intermediate for this reaction.

A simple, general synthesis of 1-alkynyldiisopropoxyboranes

Abstract A representative selection of 1-alkynyldiisopropoxyboranes has been prepared in high yields from the reaction of 1-lithio-1-alkynes and triisopropoxyboranes at −78° C, followed by treatment with hydrogen chloride.

Enantioselective ring cleavage of meso-epoxides with B-halodiisopinocampheylboranes.

Abstract : B-Halodiisopinocampheylboranes, IpcBX, in particular the bromide 1b, and the Iodide 1c, differentiate between the enantiotopic carbon-oxygen bonds of meso-epoxides to furnish 1,2-halohydrins of moderate to excellent enantiomeric purity. Thus (-)-(1R, 2R)-2-bromocyclohexanol, (-)-(1R, 2R)-2-iodocyclohexanol, (-)-(1R, 2R)-2-iodocyclohex-4-en-1-o1 and (-)-(1R, 2R)-2-bromocyclohex-4-en-1-o1 are obtained in 84%, 91%, 63% and 95% ee respectively from the corresponding meso-epoxides and haloborane reagents. Simple recrystallization from pentane then gives halohydrins of essentially 100% ee; cis-2-butene oxide and cis-3-hexene oxide furnish the corresponding (1R, 2R)-iodohydrins in 78 and 69% ee respectively. In all cases the S carbon of the meso-epoxide is selectively cleaved. This is the first example of enantioselective ring cleavage of meso-epoxides to obtain optically active 1,2-halohydrins. Keywords: Asymmetric synthesis.

A new convenient approach to the preparation of Z-1-alkenylboronates by the cis-hydrogenation of 1-alkynyldiisopropoxyboranes

Abstract Hydrogenation of 1-alkynyldiisopropoxyboranes over Lindlar catalyst in 1,4-dioxane proceeds cleanly to furnish Z-1-alkenylboronates in very high diastereoselectivity, 90–100%.

Methylborane - a remarkable unhindered monoalkylborane which achieves the controlled sequential hydroboration of representative alkenes

Abstract Methylborane, MeBH 2 , the simplest of the monoalkylboranes, possesses extraordinary hydroboration characteristics in tetrahydrofuran. In this solvent, methylborane is capable of monohydroborating the usual classes of alkenes, hindered and unhindered, to provide the simple alkylmethylboranes, RMeBH. The addition of a second equivalent of another alkene to the alkylmethylborane formed initially produces the sequential hydroboration product, RR′MeB. In all cases there is no evidence of redistributed products.