Rhodium-catalyzed enantioselective cycloisomerizations

For rhodium-catalyzed enantioselective enyne cycloisomerization and hydrosily-lation-cyclization, see (a) C. Ping,... 

Scheme 5. The first rhodium-catalyzed enantioselective enyne cycloisomerization.

Zhang s group has reported highly enantioselective cycloisomerization processes catalyzed by rhodium(i) chiral complexes (Scheme 53). For instance, (A)-BINAP gives excellent asymmetric induction in the reaction of enediyne 212 to furnish the quasi-enantiopure Alder-ene product 213.219... 

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. 

Lei A, Waldkirch JP, He M, Zhang X (2002) Highly enantioselective cycloisomerization of enynes catalyzed by rhodium for the preparation of functionalized lactams. Angew Chem Int Ed 41 4526-4529... 

One of the major advantages of the rhodium(I)-catalyzed Alder-ene reaction is that mild conditions are used to effect the cycloisomerization process thus increasing the likelihood of being able to facilitate an asymmetric reaction. In fact, Zhang has demonstrated convincingly that the Alder-ene reaction of enynes can indeed be performed with excellent enantioselectivity and with similar efficiency. These examples are highlighted below in chronological order. 

Korber N, Rominger E, Muller TJJ (2009) Novel enantioselective sequentially rhodium(I)/ BlNAP-catalyzed cycloisomerization-hydrogenation-isomerization-acetalization (CIHIA). Adv Synth Catal 351 2921-2935... 

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