Rhodium-Catalyzed Regio- and Diastereoselective [3+2] Cycloaddition of gem-Difluorinated Cyclopropanes with Internal Olefins.

Direct synthesis of gem-difluorinated carbocyclic molecules represents a longstanding challenge in organic chemistry. Herein, a Rh-catalyzed [3+2] cycloaddition reaction between readily available gem-difluorinated cyclopropanes (gem-DFCPs) and internal olefins has been developed, enabling the efficient synthesis of gem-difluorinated cyclopentanes with good functional group compatibility, excellent regioselectivity and good diastereoselectivity. The resulting gem-difluorinated products can undergo downstream transformations to access various mono-fluorinated cyclopentenes and cyclopentanes. This reaction demonstrates the use of gem-DFCPs as a type of "CF2 " C3 synthon for cycloaddition under transition metal catalysis, which provides potential strategy for synthesizing other gem-difluorinated carbocyclic molecules.

PIDA-Mediated Formal Olefinic C=C Bond Cleavage of α-Oxo-Ketene N,N-Acetals toward Substituted Oxazolines.

The hypervalent iodine reagent PhI(OAc)2 (PIDA) mediated the formal oxidative C=C bond cleavage and subsequent cyclization of internal olefins, that is, α-oxo-ketene N,N-acetals, which afforded substituted oxazolines. Isothiazoline derivatives were obtained from the reactions of α-thioxo-ketene N,N-acetals with PIDA under the same conditions. Hydrolysis of the resultant oxazoline derivatives led to highly functionalized oxazolones. A plausible mechanism was proposed based upon the formation of isothiazoline-type intermediates.

Metal-Free Direct Alkylation of Ketene Dithioacetals by Oxidative C(sp2 )-H/C(sp3 )-H Cross-Coupling.

The functionalization of internal olefins has been a challenging task in organic synthesis. This protocol provides an efficient and transition-metal-free direct oxidative C(sp2 )-H/C(sp3 )-H cross-coupling method to access tetrasubstituted olefins. The push-pull effect from the polarized olefin substrates accelerates the internal olefin C-H alkylation. Importantly, the mechanistic experimental results demonstrate that the alkanes C-H bond cleavage is the rate-determining step, and a radical pathway has been proposed for the alkylation reaction. Notably, the present protocol has excellent functional group tolerance and could be easily scaled up with good efficiency.

Regioselective, Asymmetric Formal Hydroamination of Unactivated Internal Alkenes.

We report the regioselective and enantioselective formal hydroamination of unsymmetrical internal alkenes catalyzed by a copper catalyst ligated by DTBM-SEGPHOS. The regioselectivity of the reaction is controlled by the electronic effects of ether, ester, and sulfonamide groups in the homoallylic position. The observed selectivity underscores the influence of inductive effects of remote substituents on the selectivity of catalytic processes occurring at hydrocarbyl groups, and the method provides direct access to various 1,3-aminoalcohol derivatives with high enantioselectivity.