Rhodium-Catalyzed Asymmetric Cycloisomerization Research Articles

Rhodium-Catalyzed Asymmetric Cycloisomerization of (E)-1,6-Enynes

Rhodium-Catalyzed Asymmetric Cycloisomerization of (E)-1,6-Enynes

Rhodium-Catalyzed Asymmetric Cycloisomerization and Parallel Kinetic Resolution of Racemic Oxabicycles.

While desymmetrizations by intermolecular asymmetric ring-opening reactions of oxabicyclic alkenes with various nucleophiles have been reported over the past two decades, the demonstration of an intramolecular variant is unknown. Reported herein is the first rhodium-catalyzed asymmetric cycloisomerization of meso-oxabicyclic alkenes tethered to bridgehead nucleophiles, thus providing access to tricyclic scaffolds through a myriad of enantioselective C-O, C-N, and C-C bond formations. Moreover, we also demonstrate a unique parallel kinetic resolution, whereby racemic oxabicycles bearing two different bridgehead nucleophiles can be resolved enantioselectively.

Rhodium-Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes

Rhodium-Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes

ChemInform Abstract: Rhodium‐Catalyzed Asymmetric Cycloisomerization of 1,6‐Ene‐ynamides.

The rhodium-catalyzed asymmetric cycloisomerization of heteroatom-bridged 1,6-ene-ynamides proceeded to give high yields of functionalized 3-aza- and oxabicyclo[4.1.0]heptene derivatives with high enantioselectivity, which was achieved by use of a rhodium/chiral diene catalyst. The 1,6-ene-ynamides substituted with 2-oxazolidinone and 2-azetidinone moieties at the alkyne terminus were found to display high reactivity towards the rhodium/chiral diene catalyst, where the chelate coordination of the alkyne moiety and the carbonyl oxygen of the ene-ynamides might be responsible for the high catalytic activity.

Rhodium-Catalyzed Asymmetric Cycloisomerization of 1,6-Enynes

1,6-Enynes can be converted into bicyclo[4.1.0]heptene derivatives via 6-endo-dig cycloisomerization catalyzed by π-acidic metals. Despite the high synthetic utility of this transformation, there have been only few asymmetric variants reported so far. In this paper the authors describe a rhodium-catalyzed cycloisomerization of oxygen- and nitrogen-bridged 1,6-enynes proceeding with high yields (71-94%) and enantio­selectivities (68-99% ee). Substituted tetrafluoro­benzobarrelene (TFB, 1) was found to be the optimum ligand showing high catalytic activity presumably due to its high π-accepting ability. It can be expected that the unique catalyst design will be suitable for other applications of transition-metal catalysis.

Total synthesis of platensimycin and related natural products.

Platensimycin is the flagship member of a new and growing class of antibiotics with promising antibacterial properties against drug-resistant bacteria. The total syntheses of platensimycin and its congeners, platensimycins B(1) and B(3), platensic acid, methyl platensinoate, platensimide A, homoplatensimide A, and homoplatensimide A methyl ester, are described. The convergent strategy developed toward these target molecules involved construction of their cage-like core followed by attachment of the various side chains through amide bond formation. In addition to a racemic synthesis, two asymmetric routes to the core structure are described: one exploiting a rhodium-catalyzed asymmetric cycloisomerization, and another employing a hypervalent iodine-mediated de-aromatizing cyclization of an enantiopure substrate. The final two bonds of the core structure were forged through a samarium diiodide-mediated ketyl radical cyclization and an acid-catalyzed etherification. The rhodium-catalyzed asymmetric reaction involving a terminal acetylene was developed as a general method for the asymmetric cycloisomerization of terminal enynes.