Gem-Diiodoalkanes

Reactions with other gem-diiodoalkanes under these conditions proceed in low yield however, addition of DMF (and ultrasonic irradiation) provides a very general method for alkylidenation of aldehydes with good (E)-selectivity (equation II). 

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-... 

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 Utimoto showed that reactions of aldehydes and a gem-diiodoalkane with chromium(II) chloride gave Wittig-type olefination products (Scheme 5.25) [35]. The notable points of this transformation are stereoselective ( )-alkene formation and chemoselective reaction with the aldehyde. Ketones are recovered unchanged. Instead of a gem-diiodoalkane, a-acetoxy bromide can also be used for this transformation [36]. 

Takai and coworkers showed that reactions of aldehydes and gem-diiodoalkane with chromium (II) chloride gave Wittig-type olefination product (Scheme 8.45)... 

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