Enynes, carboalumination

Since the advent of the stoichiometric Zr-promoted enyne bicyclization-carbonylation [19,20], development of its catalytic and enantioselecti ve version has been an attractive but elusive target. Although its catalytic but racemic version has recently been developed in the form of Zr-cataly zed cyclic carboalumination [39], there does not appear to be any successful report on Zr-catalyzed enantioselective enyne bicyclization-carbonylation, the closest process being that discussed in... 

Using ( )-methylalkenylalanes 140, obtained by highly stereo- and regioselective Zr-catalyzed carboalumination of alkynes, the stereochemically defined enynes 141 can also by synthesized by Pd-catalyzed cross-coupling reactions with 1-haloalkynes [Eq. (47)] [68]. 

Carboabimination The carboalumination of alkynes and enynes generates aluminacyclopentenes which can be processed into alkenylcyclopropanes and 2-cyclopentenones. 

The carbometalation reaction has been reviewed recently [28-30]. Negishi has demonstrated that zirconium(TV) complexes catalyze the carboalumination of MesAl to various alkynes and enynes [31]. Also the Zr-catalyzed asymmetric carboalumination of aUcenes (ZACA reaction) [32-34] has found important applications in the synthesis of natural products [35-37]. Especially efficient was the asymmetric synthesis of insect pheromones such as (S. / ./ ,S. / ,S)-4,6,8,10,16,18-hexamethyl-docosane (88) (Scheme 8) [38]. 

Scheme 19 Carboalumination of enynes in the synthesis of linear isoprene trimers...

In recent years, catalytic carboalumination of acetylenes has found use in the synthesis of cycloalkenes [98-101], trisubstituted olefins, homoallyl alcohols, a,p-unsaturated esters, 1,3-enyne-l,4-disilanes [102-105], a,p-unsaturated organoboron or zirconium compounds, and also natural and biologically active compounds. For example, key synthons for the preparation of prostaglandins [86,... 

---