Xiaoyi Xin

Highly Regioselective Migration of the Sulfonyl Group: Easy Access to Functionalized Pyrroles

The development of new reactions for the synthesis of diverse molecular frameworks is a challenging task in the field of modern organic chemistry. Chemistry of pyrroles continues to attract the interest of chemists, and new synthetic methods of these compounds occupy an important area of synthetic organic chemistry. In search of new routes for the synthesis of pyrroles through the design of new building blocks such as N-sulfonyl-protected azaenyne derivatives 1 (Scheme 1), we

Rhodium‐Catalyzed CH Annulation of Nitrones with Alkynes: A Regiospecific Route to Unsymmetrical 2,3‐Diaryl‐Substituted Indoles

The direct C-H annulation of anilines or related compounds with internal alkynes provides straightforward access to 2,3-disubstituted indole products. However, this transformation proceeds with poor regioselectivity in the synthesis of unsymmetrically 2,3-diaryl substituted indoles. Herein, we report the rhodium(III)-catalyzed C-H annulation of nitrones with symmetrical diaryl alkynes as an alternative method to prepare 2,3-diaryl-substituted N-unprotected indoles with two different aryl groups. One of the aryl substituents is derived from N=C-aryl ring of the nitrone and the other from the alkyne substrate, thus providing the indole products with exclusive regioselectivity.

Base-catalyzed cyclization of N-sulfonyl propargylamides to sulfonylmethyl-substituted oxazoles via sulfonyl migration.

The reaction of N-sulfonyl propargylamides in the presence of a base catalyst selectively affords 5-sulfonylmethyl oxazoles via 1,4-sulfonyl migration. Allenes have been established as the key intermediates. Experimental evidence has been provided to support a two-step mechanism in the cyclization.

From Propargylamides to Oxazole Derivatives: NIS-Mediated Cyclization and Further Oxidation by Dioxygen

NIS-mediated iodocyclization of N-sulfonyl propargylamides for the synthesis of various oxazolidines and iodoalkylidenedihydrooxazoles via a 5-exo-dig process is developed. The resulting iodoalkylidenedihydrooxazoles can be further transformed into the corresponding oxazoles in the presence of dioxygen.

Cyclization and N-iodosuccinimide-induced electrophilic iodocyclization of 3-aza-1,5-enynes to synthesize 1,2-dihydropyridines and 3-iodo-1,2-dihydropyridines.

Metal-free cyclization and N-iodosuccinimide-induced electrophilic iodocyclization of readily available 3-aza-1,5-enynes have been developed. The reactions selectively give 1,2-dihydropyridines and 3-iodo-1,2-dihydropyridines involving an aza-Claisen rearrangement and a 6π-electrocyclization step. Furthermore, the reaction could be carried out in 10 g scale for the synthesis of 1,2-dihydropyridines.

Rhodium‐Catalyzed Cyclization of Diynes with Nitrones: A Formal [2+2+5] Approach to Bridged Eight‐Membered Heterocycles

N-aryl-substituted nitrones were employed as five-atom coupling partners in the rhodium-catalyzed cyclization with diynes. In this reaction, the nitrone moiety served as a directing group for the catalytic C-H activation of the N-aryl ring. This formal [2+2+5] approach allows rapid access to bridged eight-membered heterocycles with broad substrate scope. The results of this study may provide new insight into the chemistry of nitrones and find applications in the synthesis of other heterocycles.

Cu-Catalyzed Ring Opening Reaction of 2H-Azirines with Terminal Alkynes: An Easy Access to 3-Alkynylated Pyrroles

A highly efficient Cu-catalyzed ring expansion reaction of 2H-azirines with terminal alkynes has been developed. This transformation provides a powerful method for the synthesis of 3-alkynyl polysubstituted pyrroles under mild conditions in good yields. The direct transformation process, specific selectivity, and good tolerance to a variety of substituents make it an alternative approach to the reported protocols.

DABCO-catalyzed synthesis of trifluoromethylated furans from propargyl alcohols and methyl 2-perfluoroalkynoate.

The DABCO-catalyzed reaction of propargyl alcohols with methyl 2-perfluoroalkynoate to give trifluoromethylated furans in up to 98% yield under mild conditions has been developed. The established allene-enol and control experiments indicate that the reaction should proceed through a Michael addition and Claisen rearrangement/cyclization process.

Synthesis of Polyfluoroalkyl Cyclobutenes from 3-Aza-1,5-enynes via an Aza-Claisen Rearrangement/Cyclization Cascade

A facile synthetic route to access polyfluoroalkyl functionalized cyclobutenes bearing an exo cyclic double bond from 3-aza-1,5-enynes is reported. The reaction proceeds via a thermal aza-Claisen rearrangement to give an allene-imine intermediate; subsequent cyclization affords the cyclobutene core. The kinetics of the transformation of starting material and the intermediate was studied by (1)H NMR spectroscopy, where a consecutive reaction was revealed.

Base-Catalyzed Selective Synthesis of 2-Azabicyclo[3.2.0]hept-2-enes and Sulfonyl Vinyl-Substituted Pyrroles from 3-Aza-1,5-enynes

A base-catalyzed selective cycloisomerization of 3-aza-1,5-enynes is developed. This transformation provides a facile access to highly functionalized 2-azabicyclo[3.2.0]hept-2-enes and sulfonyl vinyl-substituted pyrroles. The chemoselectivity was controlled by the substituent pattern of the substrates.