The hydroformylation of acetylenic thiophenes is readily accomplished by using the zwitterionic
rhodium catalyst (η6-C6H5BPh3)-Rh+(1,5-COD) and triphenyl phosphite in the presence of CO and
H2. This catalytic system affords, as the major product, the α,β-unsaturated aldehyde with the
aldehyde and thiophene attached to the same olefin carbon atom. Assistance of sulfur from the
heterocycle provides excellent regioselectivity and yields when the acetylenic unit is a propargyl
ether or ester, phenylacetylene, or an enyne.
The reaction of aliphatic 1-en-3-ynes with synthesis gas in the presence of the zwitterionic rhodium
complex (η6-C6H5BPh3)-Rh+(1,5-COD) and triphenyl phosphite affords formyl dienes in high
stereoselectivity. This catalytic system provides a useful method for the hydroformylation of both
nonfunctionalized and functionalized conjugated enynes under mild conditions, affording formyl
dienes in moderate to good yields.
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