Organochromium reagents reactions with carbonyl compounds

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. 

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