Allenylboron reagents

The observation that allenylboronic esters react with carbonyl compounds to afford homopropargylic compounds was first made by Favre and Gaudemar [132]. 

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Triethylaluminum, 204 Triisobutylaluminum, 205 Trimethylaluminum, 22, 205 Vilsmeier reagent-Lithium tri-r-butoxy-aluminum hydride, 342 Boron Compounds Alkyldimesitylboranes, 8 Allenylboronic acid, 36 9-Borabicyclo[3.3.1]nonane, 92 Borane-Dimethylamine, 42 Borane-Dimethyl sulfide-Sodium borohydride, 25... 

Chiralallenylboronic esters.1 These reagents can react with aldehydes to provide /(-acetylenic alcohols enantioselectivity (60-95% ee). Thus, allenylboronic acid 1, prepared as shown, reacts with aldehydes in the presence of ( + )-DET or ( + )-DlPT to give (S)-alcohols (2), whereas (R)-alcohols (2) are obtained in the presence of (-)-DF.T or ( —) DIPT, both in optical yields of 85-95%. The selectivities are lower in reaction with aryl and z,/3-unsaturated aldehydes. 

Haruta, R., Ishiguro, M., Ikeda, N., Yamamoto, H. Chiral allenylboronic esters a practical reagent for enantioselective carbon-carbon bond formation. J. Am. Chem. Soc. 1982, 104, 7667-7669. 

In addition, its high regioselective allenylboration toward diethylketone [A] and 4-f-butylmethylketone [B] as compared with the behavior of allenylmagne-sium bromide and di( -butyl)allenylboronate makes B-allenyl-9-BBN, a valuable reagent [3]. 

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