Nickel double bonds cleaving reaction

The bond between the carbon atoms a and (3 to a C-C double bond can be broken by a transition metal with formation of a Jt-allyl intermediate providing the driving force. Whereas stoichiometric reactions of this sort are yet to appear, jt-(allyl)metal intermediates are occasionally involved in catalytic C-C bond cleaving reactions. The nickel catalyzed skeletal rearrangement of 1,4-dienes involves the formation of an olefin coordinated Jt-(allyl)nickel complex (99) [118]. 

Having access to new tetrasubstituted exo-glycals, the reduction of the double bond was attempted. Monobromo exo-glycal like 6 was reduced cleanly using Raney nickel catalyst, needed to cleave the C-Br bond, but the reaction needed high pressure (10 bars) of hydrogen to obtain the C-glycosyl derivative 21 in 46-88% yield (Scheme 7). 

A nickel-catalyzed cycloaddition reaction of diketene with alkynes furnished phenylacetic acid derivatives (Scheme 7.36) [51]. Although the reaction mechanism is unclear, the C=C double bond of diketene seems to be cleaved to constitute the para-carbons (designated by black circles) of the benzene ring. 

---