Cyclopropenes carbozincation

The cw-directing ability of a 3-carboalkoxy group in cyclopropenes can be used to great advantage in net carbozincation reactions catalyzed by either Cul or Toluene is the solvent in which best diastereoselectivities are realized both THF and Et20 led to poorer results. 

As there were no previous reports on the facial selective carbozincation of cyclopropenes, Fox and coworkers [34] studied this carbometallation oriented toward the preparation of the corresponding trisubstituted cyclopropanes 120 (Scheme 10.37). 

Scheme 10.39 Copper-catalyzed carbozincation of substituted cyclopropenes directed by Evans chiral auxiliary [34].

Similarly, zincated hydrazone derivatives of type 56 undergo an intermolecular carbozincation of strained cyclopropene rings such as 57 leading to the adduct 58 with 92% yield [63]. This type of addition can be extended to ethylene ]63c]. It proceeds with an excellent stereoselectivity allowing the enantioselective synthesis of a-substituted ketones. Allylic zinc species also add to cyclopropenone acetals... 

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