Enantioselective Rhodium-Catalyzed Allylic Alkylations

Enantioselective transition metal-catalyzed allyhc alkylation has stimulated immense interest due to its potential synthetic utihty [1 b]. Although excellent enantioselectivities have been obtained for a wide variety of cychc and acyclic aUyhc alcohol derivatives, using a wide range of chiral transition metal complexes, the ability to also control regioselectivity has proven challenging. In hght of the excellent selectivities observed for rhodium-catalyzed allyhc substitution, it would seem reasonable to assume that the enantioselective rhodium-catalyzed version may provide the definitive solution to this problem. 

We would like to acknowledge the experimental and intellectual contributions of our co-workers in the catalysis subgroup. In particular, we would like to highlight the seminal contributions of our former colleagues Lawrence J. Kennedy, Kristofer K. Moffett, Jade D. Nelson, John E. Robinson, and Daisuke Uraguchi. We sincerely 

1 For book chapters on metal-catalyzed allylic substitution, see (a) Tsuji, J. in Palladium Reagents and Catalysts Innovations in Organic Synthesis Wiley New York, 1996, Ch. 4, pp. 290-404. (b) Trost, B.M. Lee, C. in Catalytic Asymmetric Synthesis, 2nd ed. OjiMA, I., Ed. Wiley-VCH New York, 2000, Ch. 8, pp. 593-649. 

3 For lead references on other transition metal-catalyzed allylic substitution reactions, see (a) Cobalt Bhatia, B. Reddy, M.M. Iqbal, J. Tetrahedron Lett. 1993, 34, 6301. 

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Tab. 10.12 Enantioselective rhodium-catalyzed allylic alkylations with dimethyl malonate.

In 2003, Hayashi and his co-workers found that highly enantioselective rhodium-catalyzed allylic alkylation took place with l-aryl-2-propenyl acetates by using an achiral /3-diketonate ligand for the rhodium complexes in the presence of (diphenylphosphino)binaphthyloxazoline 60b. Fine-tuning of the /3-diketonate part resulted in enhancement in enantioselectivity up to 97% ee (Equation (49)). " ... 

As an extension of these studies on the use of sulfoximines in asymmetric reductions, BlNOL-derived phosphino sulfoximines of the 105 type were tested in both rhodium-catalyzed hydrogenations (yielding optically active diesters 104 or amino acid derivatives Scheme 2.1.1.35) and palladium-catalyzed allylic alkylations (not shown) in collaboration with Reetz and Gais [81, 82]. Here, enantioselectivities of up to >99 and 66% ee, respectively, were achieved. 

The Rh-BINAP-catalyzed intramolecular Alder-ene cycloisomerization is very rapid and, therefore, sequentially Rh-catalyzed sequences for the efficient enantioselective generation of five-membered carbo- and heterocycles were envisioned. Korber et al. [21] reported the enantioselective rhodium-catalyzed cycloisomerization of alkyl and (hetero)aryl alkynyl allyl alcohols for the generation of aldehyde-bearing chiral 4-alkyl 3-alkylidene THFs and tetrahydro-furanones, which were converted into a,P-unsaturated carbonyl side chains in a one-pot manner via a concluding Wittig olefination in good yields. 

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