Science of Synthesis

Poli, R.; Smith, K. M., Science of Synthesis, (2003) 2, 310.

The organochromium(III) compound may be either isolated before the addition to the car­bon­yl compound or prepared in situ, as shown in ‌Scheme 28‌. Tri­phen­yl­tris(tet­ra­hy­dro­fu­ran­)chromium(III) is able to react with ke­to­nes, viz. pentan-3-one (‌67‌) and cy­clo­hexanone.[‌122‌] On the other hand, chlo­ro­di­al­kyl and di­chlo­ro­al­kyl derivatives are highly al­de­hyde selective, while al­kyl­pentaaquachromium(III) is unreactive. The al­kyl­di­chlo­ro­chromium(III) reagent is particularly useful as it can be readily generated in situ by transmetalation from chromium(III) chlo­ride and a Grignard reagent; see the formation of ‌68‌.[‌123‌] These reagents are able to transfer the al­kyl group to the organic substrate even in an alcoholic medium or in the presence of water.[‌124‌] Di­chlo­ro[­(tri­meth­yl­si­lyl)­meth­yl­]chromium(III) allows an al­de­hyde-selective alkenation process after acid hy­dro­lysis.[‌125‌] This procedure has been more recently supplanted by those described in the following variations.

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References