Alkynes oxycarbonylation

From Alkenes to Alkynes Bismuth-Catalyzed Carbo-oxycarbonylations. 137... 

The synthesis of flavones and chrotnones is possible by palladium-catalyzed intermolecu-lar cis oxycarbonylation of terminal alkynes with 2-iodophenols62. 

Another example of a regiodivergent qrdiTation of a racemic substrate is shown in Scheme 6.30 [51]. Racemic 140 was treated with Pd in the presence of chiral hgand 141, and the crude reaction mixture was oxidized using Dess-Martin periodinane (DMP) to form the bicychc products 143 (42% ee) and 144 (95% ee). Formation of the initial cydized product 142 is beheved to occur via the hemiacetal resulting from reversible addition of isopentanol to the ketone, followed by internal oxycarbonylation of the alkyne. Lower enantiomeric purity in 144 was observed when less bulky alcohols were used in place of the isopentanol. In contrast, the product 143 does not incorporate the alcohol and htde variation in enantiomeric excess was observed using different alcohols. 

In a similar manner, alkynes with a terminal triple bond cyclize to tetrahydropyrans by an oxycarbonylative... 

SCHEME 15.7. Oxycarbonylation of alkynes as the key step in the synthesis of callipeltoside C. 

---