Boron-zinc exchange

Functionalized olefins may be converted to the corresponding diorganozinc compounds via hydroboration and subsequent boron-zinc exchange, as shown in Scheme 4.28... 

For internal olefins, the hydroboration step is slower, taking days rather than hours, and in this case the boron-zinc exchange requires the use of Zn(Pr )2 (Scheme 5). The reaction is stereospecific, provided that the diisopropylzinc is metal halide free.29,30... 

Scheme 2.31. Boron-zinc exchange for the preparation of chiral organozinc reagents.

Scheme 2.32. Preparation of polyfunctional primary dialkylzinc compounds by boron-zinc exchange.

The RzZn reagents are readily prepared from the corresponding (functionalized) alkene by hydroboration and subsequent boron-zinc exchange, according to the... 

Scheme 7.8. Nickel-catalyzed 1,4-addition, using alkene hydroboration and boron-zinc exchange.

A combination of a substitution reaction with a chlorophosphine followed by a hydroboration and boron-zinc exchange allows the preparation of the mixed 1,2-diphosphine 207 in good yield (Scheme 62). ... 

Boron-sulfur bonds, addition, to alkynes, 10, 778 Boron trihalides, in boron compound synthesis, 9, 146 Boron-zinc exchange and copper-catalyzed substitutions, 9, 518 for organozinc halide preparation, 9, 89 Borostannylation, enynes, 10, 334... 

Pyrrolidinylmethanols derived from (S)-proline have been employed in the zinc-catalysed addition of arylboronic acids to aromatic aldehydes, giving ees up to 98%.242 An arylzinc species is generated via a boron-zinc exchange, avoiding the need for expensive diphenylzinc. 

The asymmetric arylation of aldehydes in the presence of a catalytic amount of chiral amino alcohol111 or of chiral tertiary aminonaphthol112 has been described. The reactive arylzinc species have been generated in situ from a boron-zinc exchange instead of employing the more expensive diphenylzinc. The chiral diaryl carbinols have been obtained in high yields and ees. 

Remarkably, by utilizing /-Pr2Zn for the boron-zinc exchange reaction, configurational well defined secondary dialkylzinc reagents, like 34, have been prepared for the first time (Scheme l.ll).37... 

Preparation of dioctylzinc by boron-zinc exchange and its copper-mediated coupling with an electrophile preparation of ethyl 2-nonylacrylate... 

Besides the iodine-zinc exchange reaction, the boron-zinc exchange reaction proves to be an excellent method for preparing a broad range of polyfunctional diorganozincs (Scheme 5.8). The exchange reaction for primary diethylalkyl boranes proceeds at room temperature and is complete within a few minutes. 

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