Aldol-Type Coupling under Neutral Conditions

Design of Reactions Starting from Insertion into a Rh-H Bond 

Aidoi-Type Coupiing under Neutrai Conditions 

However, since both a,yS-unsaturated ketone 11 and an aldehyde are readily hydrosily-lated in the presence of a rhodium complex, the interaction of these substrates with the metal complex must be controlled. Experimental studies demonstrated that Et2MeSiH and Rh4(CO)i2, modified by MePh2P, provided the requisite combination to furnish 15a in acceptable yield, as demonstrated in the reaction of 3-buten-2-one 11a (R = CH3, r2 = r3 = h) with benzaldehyde (Eq. 3 Tab. 6.1) [8]. 

Morken and co-workers have reported the highly enantioselective version of this reaction, albeit with low efficacy in the aldol-type coupling [8d, e]. Unfortunately, we obtain low enantioselectivity ee 2-4%) using chiral rhodium complexes under our reaction conditions. An intramolecular adaptation has led to new opportunities in cobalt-catalyzed carbocyclizations, wherein the use of PhSiHs was essential for smooth ring formation (Eq. 4) [9]. The identical products were also formed by a combination of [Rh(COD)2]OTf/(p-CE3Ph)3P and molecular hydrogen [10]. 

Apparent Hydrocarbamoylation to a, -Enoates and Mannich-Type Coupling 

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