Rw. Barnhart et al., ASYMMETRIC CATALYSIS - ASYMMETRIC CATALYTIC INTRAMOLECULAR HYDROACYLATION OF 4-PENTENALS USING CHIRAL RHODIUM DIPHOSPHINE CATALYSTS, Journal of the American Chemical Society, 116(5), 1994, pp. 1821-1830
Catalysts of the type [Rh(chiral diphosphine)](+) convert 4-substitute
d 4-pentenals into the corresponding 3-substituted cyclopentanones wit
h generally high turnover numbers and frequencies at 25 degrees C. The
enantioselectivities of various substituted 4-pentenals with two chir
al diphosphines have been explored. It was found that with the binap c
atalyst, almost complete enantioselectivity is observed for 4-pentenal
substrates bearing 4-substituted tertiary substituents and for ester
groups. Ketonic substituents give very high enantioselectivities. The
mechanism of intramolecular hydroacylation has been explored, and it i
s suggested that an important consideration for obtaining high turnove
r frequencies is related to the acyl-alkyl reductive elimination mecha
nism which is inferred to occur by a process similar to ester hydrolys
is. The origin of the enantioselection is discussed in terms of the in
teractions between the phenyl groups of the phosphine and the substitu
ent of the pentenal.