Preparation of zincates

Similarly, alkenylzirconium species prepared by the hydrozirconation of alkynes add in a conjugated fashion to enones. Formation of an intermediate zincate prior to transmetalation to the copper species facilitates the Michael addition (Scheme 2.62) [135]. This methodology has been applied to the preparation of protected misoprostol 129 (Scheme 2.63) [136, 137]. 

SCHEME 54. Preparation and uses of zincates on the solid phase... 

SCHEME 16. Preparation of ailyl- and benzylzinc derivatives by oxidative zincation... 

C. Preparation of Mixed Zincates by Halogen-Zinc Exchange Reaction. . . 688... 

The chiral organocopper compound (186) adds diastereoselectively to 2-methyl-2-cyclopentenone, allowing the preparation of optically active steroid CD-ring building blocks (Scheme 68).202-204 A related method was applied to a synthesis of the steroid skeleton via an intramolecular (transannular) Diels-Alder reaction of a macrocyclic precursor.203 Chiral acetone anion equivalents based on copper azaeno-lates derived from acetone imines were shown to add to cyclic enones with good selectivity (60-80% ee, after hydrolysis).206-208 Even better ee values are obtained with the mixed zincate prepared from (187) and dimethylzinc (Scheme 69). Other highly diastereoselective but synthetically less important 1,4-additions of chiral cuprates to prochiral enones were reported.209-210... 

Copper catalysed addition of a (3-zincated phosphonate to an electrophile preparation of dimethyl 2-(cyclohex-1-en-3-on-1-yUpentanephosphonate10... 

---