Organochromium compounds reagents

Organochromium compounds prepared from chromium(III) salts and organometallic reagents have been shown to possess carbanionic character and provide the first examples of organochromium additions to carbonyl substrates. Sneeden and cowoikers reported that triphenyltris(tetrahydrofuran)chro-... 

The addition to a,p-unsaturated aldehydes proceeds exclusively in a 1,2-fashion (equation 24). This regiochemical preference is general for all organochromium compounds. The addition to 4-r-butylcyclo-hexanone (32) occurs predominantly via equatorial addition (equation 25), as it provides (33) and (34) in an 88 12 ratio. Allylchromium is one of the most efficient reagents for this transformation (Table 1). 

The one-pot Barbier-type addition of alkenyl, aryl, allyl, vinyl, propargyl, alkynyl, or allenylchromium compounds to aldehydes or ketones is known as the Nozaki-Hiyama-Kishi (NHK) reaction. An excellent review by Furstner published in 1999 detailed the exhaustive literature on the carbon-carbon bond formations involving organochromium(III) reagents. This chapter will present major developments and examples of recent carbon-carbon bond formation methodology and improvements as well as their use in natural products synthesis since 1999. 

The Nozaki-Hiyama-Kishi (NHK) reaction, first reported in the late 1970s, has become an important and versatile carbon-carbon, bond-forming process, involving the nucleophilic addition of organochromium(III) reagents to carbonyl compounds (Scheme 12.1). ... 

The practical use of chromium(II) chloride in organic synthesis was begun by Hiyama and Nozaki in 1976. They used anhydrous chromium(II) chloride for the reduction of allylic halides to get allylic chromium reagents [47]. Since then, useful C-C bond formation reactions between organic halides and carbonyl compounds, which were mediated by chromium(II) salt have been developed. The most important features of these reactions were chemoselectivity and stereoselectivity. In these transformations, treatment of organic halides with chromium(II) salt was considered to afford the intermediary organochromium compounds although these compounds have not been isolated. As described in the previous section, reduction of gem-dihalides with chromium(II) salt may afford gem-dichromium species. 

Takai, K., Nozaki, H. Nucleophilic addition of organochromium reagents to carbonyl compounds. Proceedings of the Japan Academy,... 

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