Hydroboration diorganozinc preparation

The hydroboration of dienic silyl enol ethers, such as 124, with LItBH leads to organob-oranes which can be converted to new diorganozincs, such as 125 (Scheme 42) . More importantly, this method allows the preparation of chiral secondary alkylzinc reagents. 

A. Preparation of functionalized diorganozinc by hydroboration and boron-zinc... 

More importantly, this method allows the preparation of chiral secondary alkylzinc reagents. Thus, the hydroboration of 1-phenylcyclopentene with (-)-IpcBHj (99% ee) [107] produces, after crystallization, the chiral organoborane 126 with 94% ee. The reaction of 126 with Et2BH replaces the isopinocampheyl group with an ethyl substituent (50 °C, 16h) and provides after the addition of t-Pr2Zn (25 C, 5 h), the mixed diorganozinc 127. Its stereoselective allylation leads to the trans-disubstituted cydopentane 128 in 44% yield (94% ee trans cis= 98 2) Scheme... 

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