Hydroborations aldehydes, pinacolborane

Hydroboration of (5) with an excess of pinacolborane at room temperature for 3 days in the absence of solvent followed by oxidation with PDC in the presence of an excess of TMSC1 led to the aldehyde (4h) and the ketone (4i) (75 % and 50 % from (5h) and (5i) respectively after bulb to bulb purification) l2,13, Several other (3-kcto vinylboronates were obtained in good yields via the addition of organozinc or organocuprates to the aldehyde (4h) followed by a PCC oxidation of the corresponding allylic alcohols14. 

Hydroboration of carbonyl compounds by pinacolborane is chemoselectively catalysed by titanocene bis(catecholborane) (A). Aryl aldehydes and ketones produce alkoxypinacolboronate esters (B) in moderate to high yields. The facile hydrolysis of B over silica affords alcohols in good yields. The catalytic hydroboration of electron-poor acetophenones is faster than that for electron-rich acetophenones. Computational studies with benzophenone and benzaldehyde indicated that hydroboration is spontaneous and probably proceeds via Ti metallacycle intermediates whose structures... 

Hydroboration of aldehydes and ketones by pinacolborane is aided by a pre-catalyst cycle involving a heteroleptic magnesium alkyl complex and the ketone. ... 

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