Asymmetric Catalysis on the Intramolecular Cyclopropanation of α-Diazo-β-keto Sulfones

Abstract

This work describes the development of a highly enantioselective asymmetric catalysis on the intramolecular cyclopropanation of alpha-diazo-beta-keto sulfones. We have found that the catalytic asymmetric intramolecular reactions of alpha-diazo-beta-keto sulfones generally proceed with high enantioselectivity when the alpha-diazo-beta-keto mesityl sulfone is used with the newly prepared ligand 2e. The absolute configuration of products has been determined by X-ray crystallographic analysis, and the outcome of the enantioselectivities is explained well by our proposed models A and B. The products possess great potential for natural product synthesis because (1) many different chemistries of cyclopropane, ketone, and sulfone are available, and (2) the products are generally highly crystalline, facilitating the supplies of enantiomerically pure synthetic intermediates.

Using a Tripod as a Chiral Chelating Ligand: Chemical Exchange Between Equivalent Molecular Structures in Palladium Catalysis with 1,1,1‐Tris(oxazolinyl)ethane (“Trisox”)

“…and 2,2-bis[(4S)-4-isopropyloxazolin-2-yl]-1,3-diphenylpropane, [38] as well as (4S)-2-bromo-4-benzyloxazoline, [39] (4R,5S)-2-bromo-4,5-indanediyloxazoline, [39] (4R)-2-bromo-4-phenyloxazoline [39] were synthesised according to literature procedures. 2,2-Bis[(4S)-4-isopropyloxazolin-2-yl]-4,4-dimethylpentan-3-one, 2,2-bis[(4S)-4-isopropyloxazolin-2-yl]-1-phenylpropan-1-one, 2,2-bis[(4S)-4-isopropyloxazolin-2-yl]-1,3-di(naphth-2-yl)propane and 2,2-bis[(4S)-4-isopropyloxazolin-2-yl]-1,3-di(pyrin-2-yl)propane were obtained according to previously published protocols.…”

Rhodium‐Catalyzed Asymmetric Intramolecular Cyclopropanation of Substituted Allylic Cyanodiazoacetates

“…To our knowledge, the only report of such an enantioselective cycloaddition (98% ee) is a Cu(I)-catalyzed intramolecular cyclopropanation of a-diazo-b-keto sulfones (Scheme 1). [3] Müller has also reported an enantioselective intramolecular cyclopropanation of a malonate derivative, however, the optimized conditions led to a product having 83% ee in only 24% yield (Scheme 1).…”

Development of Catalytic Asymmetric Intramolecular Cyclopropanation of α-Diazo-β-Keto Sulfones and Applications to Natural Product Synthesis

“…Therefore, we began to investigate asymmetric catalysis for the intramolecular cyclopropanation of a-diazo-b-keto sulfones because (a) the sulfonyl group is apparently sterically different from the keto group, implying that good enantioselectivity would emerge; (b) the sulfonyl group is a better surrogate for the ester group because of its utility; and (c) a-diazo-b-keto sulfones are easily prepared and stable, fulfilling the requirements for natural product synthesis. Only one example had been reported for the CAIMCP of a-diazo-b-keto sulfones prior to our report, 5,7,8 and the enantiomeric excess observed for 4a (see Table 1) was low at about 12% ee. 9 Therefore, we first examined the reaction of the simple substrate 3a in the presence of the easily accessible ligand 2a ( Table 1, entry 1).…”