Gem-Dichromium reagents

Olefination of aldehydes with gem-dichromium reagents.1 Reduction of 1,1-diiodoethane with CrCl2 in THF provides a 1,1-dichromioethane reagent (a) that reacts with aldehydes to furnish products of ethylidenation in 80-99% yield with high (E)-selectivity (equation I). 

Table 17 Synthesis of f )-Alkenylsilanes (276) from Aldehydes (275) and gem-Dichromium Reagents (274)...

Okazoe, T., Takai, K., Utimoto, K. (E)-Selective olefination of aldehydes by means of gem-dichromium reagents derived by reduction of gem-diiodoalkanes with chromium(ll) chloride. J. 7 m. Chem. Soc. 1987, 109, 951-953. 

Takai and coworkers have reported that the formation of alkyl-gem-dichromium compounds (269) can be achieved by the CrCk reduction of gem-diiodoalkanes (268 equation 90). These reagents add to aldehydes and affcnd alkylidenation products (271) and (272) efficiently and with high levels of ( )-al-... 

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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