PALLADIUM-CATALYZED PHENYLATION OF ENOL ETHERS AND ACETATES

Reaction of iodobenzene with 3, 4-dihydro-2H-pyran in the presence of diacetatobis(triphenylphosphine)palladium(II) and triethylamine at 100 °C occurred with high regioselectivity yielding 2-phenyl-3, 4-dihydro-2H-pyran(63%) as the sole, isolated product. Similar reaction of iodobenzene with ethyl vinyl ether exhibited little regioselectivity, producing low yields of 1-ethoxyethylbenzene and (E)- and (Z)-2-ethoxyethenylbenzenes. The difference in regioselectivities observed for phenylation of these cyclic and acyclic enol ethers is attributed to the relatively greater electronic effect and the lesser steric difference between the olefinic carbons of the cyclic 3, 4-dihydro-2H-pyran as compared with the acyclic ethyl vinyl ether. Similar palladium-catalyzed phenylationof vinyl acetate yielded, for a variety of reaction times and temperatures, mixtures of six products: styrene, (E)- and (Z)-phenylvinyl acetates, trans-and cis-stilbenes, and biphenyl. © 1979, American Chemical Society. All rights reserved.