[3 + 2] A 1,3-Dipolar cycloaddition of C,N-cyclic azomethine imines with allyl alkyl ketones has been achieved. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. An array of tetrahydroisoquinoline derivatives is generally constructed with good diastereoselectivities and enantioselectivities (up to >25:1 dr, >95% ee). Moreover, the absolute configuration of the product was previously determined by using the quantum electronic circular dichroism calculation and ECD spectrum method.
Under the catalysis of PhCO2H, the 1,3-dipolar [3+2] cycloaddition between pyrazolone-based olefins and N, N’-cyclic azomethine imines proceeded readily, thus delivering structurally novel spiropyrazolones with up to 98% yield and >20:1 dr. The relative stereochemical configuration of the obtained spiropyrazolones was unambiguously assigned by X-ray single crystal structure analysis. The diastereoselective formation of the title spiropyrazolones was interpreted by the hypothesized reaction mechanism.
The [3+2] and [3+3] regioselective cycloaddition reactions of azomethine imines with activated cyclopropanes have been developed using two different Lewis acids. Scandium (III) triflate serves as a catalyst for the [3+2] cycloaddition reactions of azomethine imines with cyclopropanes to form tetrahydropyrazolone derivatives and tricyclic tetrahydrofuran derivatives in moderate yields. In complementary to this, novel [3+3] cycloaddition reactions of azomethine imine with activated cyclopropanes have been developed using EtAlCl2 as a Lewis acid to form hexahydropyridazinone derivatives in high regioselectivity.
Catalyst-free and atom-economical 1,3-dipolar cycloaddition of C,N-cyclic azomethine imines: Facile synthesis of isoquinoline-fused spirocycles