Carbon-oxygen bond formation cascade reactions

It is worth mentioning that some precursors easily catalyze the reductive carbonylation of alkynes from the C0/H20 couple. Here, the main role of water is to furnish hydrogen through the water-gas-shift reaction, as evidenced by the co-production of CO2. In the presence of Pd /KI terminal alkynes have been selectively converted into furan-2-(5H)-ones or anhydrides when a high concentration in CO2 is maintained. Two CO building blocks are incorporated and the cascade reactions that occur on palladium result in a cyclization together with the formation of an oxygen-carbon bond [37,38]. Two examples are shown in Scheme 4. 

The tricyclic product is formally a [2-l-2-l-2]-cycloaddition where the alkene is adding to the carbonyl-oxygen and a-carbon in dienone 3 concomitant with o-bond formation between the carbonyl-carbon and the P-enone carbon. This mode of reactivity, 1,3-addition of an alkene to an enone, is unprecedented, and a specific mechanistic explanation for this process is currently lacking. Oxyallyl 37 and cis trans-dienone 40 do not appear to be involved in this process, and the reactive intermediate being trapped must appear earher in the reaction cascade. It is unclear whether this intermediate is an excited state of 36 or possibly an oxabicyclobutane 49. In either case, it is curious why this reaction is seen with 2,3-dimethyl-2-butene and not with any of the other alkene traps. 

The diastereo-selective synthesis of protected CM-2-aminocyclopropanols has been performed by the reaction of A-f-butylsulfinyl ketimines with acylsilanes. A cascade transformation involving the formation of two carbon-carbon bonds and an oxygen-silicon bond is a key feature of this reaction. 

---