Enantioselective [2+1] Cycloaddition: Cyclopropanation with Zinc Carbenoids

Stereoselective Cyclopropanation Reactions

“…The observation that diiodomethane reacts with zinc to give an iodomethylzinc species was first reported in 1929 by Emschwiller . However, about 30 years later, Simmons and Smith were the first to appreciate that this reagent (IZnCH 2 I) could be used for the stereospecific conversion of alkenes to cyclopropanes (eqs 5 and 6) . The cyclopropanation reactions using these reagents are characteristically stereospecific, proceeding through a “butterfly-type” transition structure …”

Ultraviolet Photolysis of CH2I2in Methanol: O−H Insertion and HI Elimination Reactions To Form a Dimethoxymethane Product

“…Polyhalomethanes such as CH 2 I 2 have been widely used as reagents for addition (such as Kharasch addition) and cyclopropanation of olefins and diiodomethylation of carbonyl compounds. − The ultraviolet photolysis of CH 2 I 2 in the presence of olefins 9,17,19,20 leads to formation of cyclopropanated products with a high stereospecificity and a lack of C−H insertion that indicates the carbenoid species is not a free carbene. Ultraviolet photolysis of some other polyhalomethanes such as CHFBr 2 , CHClBr 2 , CHBr 3 , and CHI 3 in the presence of olefins was also found to produce some halocyclopropanated products. , Polyhalomethanes can also be activated by metal atoms to form Simmons-Smith type reagents 1-8,10,14,15,21-29 to carry out a wide range of cyclopropanation reactions.…”

Palladium(II)-Catalyzed Highly Enantioselective C–H Arylation of Cyclopropylmethylamines

“…In addition to the aforementioned fundamental challenges, the widespread presence of cyclopropyl moieties in drug and agrochemical molecules provided further motivation for us to develop enantioselective arylation of cyclopropyl C–H bonds in cyclopropylmethylamines (Figure ) . Notably, synthesis of chiral cis -aryl-cyclopropylmethylamines remains a significant challenge …”