Utilization of Vinylidene to Alkyne Conversion

In this short section are described two unique examples utilizing the inverse transformation of vinylidene complexes to alkynes. 

Wulff et al. recently reported another unique example of this inverse transformation [35]. Thus, treatment of a, P-unsaturated Fischer carbene complexes 138 with an isopropoxy group on the carbene carbon with ketene acetal 139 at 80 °C in THF under CO pressure gave 4-pentynoate derivatives 140 in good yield. The reaction was proposed to proceed through 1,4-addition of ketene acetal to the carbene complex to give a zwitterionic intermediate 141. This underwent internal 

Synthetic Reactions Utilizing Other Kinds ofVinylidene Complexes of Croup 6 Metals 

As described in this chapter, vinylidene complexes of Group 6 metals have been utilized for the preparation of various synthetically useful compounds through electrophilic activation or electrocyclization of terminal alkyne derivatives. These intermediates are quite easily generated from terminal alkynes and M(CO)6, mostly by photo-irradiation and will have abundant possibilities for the catalytic activation of terminal alkynes. Furthermore, it should be emphasized that one of the most notable characteristic features of the vinylidene complexes of Group 6 metals is their dynamic equilibrium with the it-alkyne complex. Control of such an equilibrium would bring about new possibilities for unique metal catalysis in synthetic reactions. 

6 Mayr, A., Schaefer, KG. and Huang, F.Y. (1984) Journal of the American Chemical Society, 106, 1517-1518. 

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