Carbonylative carbotricyclizations

In the contrast to the SiCaT reaction of triynes vide supra), when an enediyne has an olefin at the terminal position a novel silicon-initiated carbonylative carbotricyclization (CO-SiCaT) reaction takes place, incorporating CO into the product [52], As Scheme 7.24 indicates, the reaction of dodec-ll-ene-l,6-diynes 82 catalyzed by Rh(acac)(CO)2 under 1 atm. CO affords the corresponding cyclopenta[e]azulenes 83 in good to excellent yield. 

The first attempt to construct a condensed core was a unique silicon-initiated (CO-SiCaT) reaction of carbonylated carbotricyclization of enediynes 2.314 [154, 161]. The 5-7-5 fused tricyclic products can be produced from the same type enediynes and CO through also by the rhodium-catalyzed intramolecular [2+2+2+1] cycloaddition [154, 160]. Reaction of dodeca-ll-ene-l,6-diyne 2.314 or heteroatomic analogues with a hydrosilane catalyzed by Rh(acac)(CO)2 at ambient temperature and pressure affords the corresponding fused 5-7-5 tricyclic system with a seven-membered lactone ring, 5-oxo-l,3a,4,5,7,9-hexahydro-6H-cyclopenta[e]azulenes 2.315 or related heteroanalogs in a yield from good to excellent (50-98%) (Scheme 2.104) [154]. 

Scheme 2.105 explains the mechanism of the CO-SiCaT initiated carbonyl-carbotricyclization [154]. 

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