Lithium chloroallylides

For application in organic synthesis, the regiochemistry of insertion of carbenoids into un-symmetrical zirconacydes needs to be predictable. In the case of insertion into mono- and bicydic zirconacydopentenes where there is an wide variety of metal carbenoids insert selectively into the zirconium—alkyl bond [48,59,86], For more complex systems, the regiocon-trol has only been studied for the insertion of lithium chloroallylides (as in Section 3.3.2) [60]. Representative examples of regiocontrol relating to the insertion of lithium chloroal-lylide are shown in Fig. 3.2. 

The following protocols describe the synthesis of zirconacycle 45 from 1,6-heptadiene and its characterisation by NMR spectroscopy. Zirconacycle 45 is then elaborated into alcohol 49 by reaction with carbon monoxide, and alcohol 54 (R = Ph) by tandem insertion of lithium chloroallylide and benzaldehyde. 

Tandem insertion of lithium chloroallylide and benzaldehyde into the zirconacycle (Structure 45) to give alcohol (Structure 54) (R = Ph)... 

The regioselectivity of insertion of lithium chloroallylides (allyl carbenoids) into a wide variety of unsymmetrical zirconacycles has been determined. In all but one case a single regioisomer was obtained. A combination of steric and electronic effects was needed to explain the results and imply that the carbenoid was acting predominantly as an electrophilic species. The first carbenoid insertion into a zirconacyclopentadiene has been noted. " ... 

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