Organochromium reagents

Allylic bromides can also serve as progenitors for nucleophilic organochromium reagents. An elegant example is found in Still and Mobilio s synthesis of the 14-membered cembranoid asperdiol (4) (see Scheme 2).7 In the key step, reduction of the carbon-bromine bond in 2 with chromium(n) chloride in THF is attended by intramolecular carbonyl addition, affording a 4 1 mixture of cembranoid diastereoisomers in favor of the desired isomer 3. Reductive cleav-... 

Nozaki-Hiyama-Kishi (NHK) reactions215,216 are well known and often employed as a useful method for the synthesis of natural products by coupling of allyl, alkenyl, alkynyl, and aryl halides or triflates with aldehydes. The organochromium reagents are prepared from the corresponding halides or triflates and chromium(ll) chloride, and are employed in polar aprotic solvents (THF, DMF, DMSO, etc.). Subsequently, it was found that nickel salts exhibited a significant catalytic effect on the formation of the C-Cr bond217,218 (Equation (19)). 

Application of Organochromium Reagents to Induce Conjugate Addition... 

For a comprehensive review of carbon-carbon bond formation with organochromium reagents, see (a) Fiirstner, A., Chem. Rev. 1999, 99, 991. (b) Wessjohann, L. A., Scheid, G., Synthesis 1999, 1. 

Organochromium reagents generated from alkyl-lithiums or -magnesiums and C1CI3 react with aldehydes selectively in the presence of ketones (equation RLi-UCU reagents, developed recently,... 

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