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A highly regioselective inverse electron-demand aza-Diels-Alder reaction of α,β -unsaturated thioesters with 1,2-diaza-1,3-dienes generated in situ from α-halogeno hydrazones was developed. With α,β-unsaturated thioesters as C═S dienophiles, the developed protocol enables the formation of diverse 3,6-dihydro-2 H -1,3,4-thiadiazine derivatives in excellent yields. In the presence of lithium aluminum hydride, 3,6-dihydro-2 H -1,3,4-thiadiazine derivatives could be further transformed into 5,6-dihydro-4 H -1,3,4-thiadiazines in good yields.

An unprecedented (3+1) cyclization of α-nitrosostyrenes, generated in situ from α-bromooximes, and N -tosyloxycarbamates was developed, which enables the synthesis of a range of structurally unique and hitherto unexplored 2,3-dihydrodiazete N -oxides in moderate to high yields. The products possess a highly strained four-membered ring structure containing two nitrogen atoms. The synthetic applicability of the products was also demonstrated by many important conversions to diverse nitrogen-containing compounds.

An efficient inverse electron-demand aza-Diels-Alder reaction of cyclic enamides and 1,2-diaza-1,3-dienes, which could be readily formed in situ from α-halogeno hydrazones and a base, has been successfully developed. With the developed approach, a wide range of fused polycyclic tetrahydropyridazines were smoothly obtained in up to 99% yield under benign reaction conditions. This reaction concept was also extended to acyclic enamide substrates for accessing 1,4,5,6-tetrahydropyridazines. A gram-scale experiment and further derivatizations of the polycyclic tetrahydropyridazine products were also conducted to verify the practicability of the methodology.

A sequential [4 + 2]/[2 + 1] annulation of α-aryl vinylsulfoniums with 2-aminochalcones and 2-(2-aminobenzylidene)-1 H -indene-1,3(2 H )-dione is reported that affords a series of cyclopropane-fused tetrahydroquinolines. The salient features of this novel and practical transformation include high efficiency, transition-metal-free nature, operational simplicity, and outstanding functional group tolerance.