Reaction of cyclic secondary amines with 1-alkynes and copper(I) chloride at 110-120 °C gives the corresponding alkynylcopper complex, which adds to the iminium ion intermediate formed in situ by hydroamination of 1-alkynes to give the corresponding propargylamine derivatives in up to 94% yield and 99% regioselectivity. The diastereomerically pure chiral propargylamines were obtained in 23-89% yield using optically active 2-benzyl morpholine and N-methyl camphanyl piperazine. These chiral propargylamines are readily converted to the corresponding trisubstitued chiral allenes in 71-89% yields with up to 99% ee upon reaction with ZnBr2 at 120 °C. The results are discussed considering mechanisms involving diastereoselective addition of alkynylcopper complex formed in situ to iminium ions formed in situ regioselectively to produce the corresponding propargylamines, which in turn give the chiral allenes with very high enantioselectivity via an intramolecular 1,5-hydrogen shift in the presence of zinc bromide.

α-Halohydrazones/ketoximes are transformed into trisubstituted pyrazoles/disubstituted isoxazoles by treatment with phosphine, acyl chloride, and a base. Mechanistic investigations revealed the in situ formation of azo/nitroso olefin intermediates which underwent a tandem phospha-Michael/N-or O-acylation/intramolecular Wittig reaction to afford the heteroarenes in moderate to good yields. Further, proper functionalization of α-haloketoximes and a change of conditions allowed the chemoselective synthesis of chromenone-oximes as well as rearranged isoxazoles, thereby realizing a diversity-oriented synthesis.

Zinc chloride catalyzed reactions of chiral piperazine derivatives 4a–d with 1‐alkynes and aldehydes give chiral propargylamines in 67–95 % yields with up to 99:1 dr. The chiral propargylamines are converted into chiral allenes by using zinc bromide in short reaction times (1–2 h) in high enantioselectivities (up to 99 % ee) in good yields (up to 89 %). The chiral piperazines are recovered in good yields (79–86 %) by reduction of the imine byproducts in situ by using NaBH4. Unexpectedly, the chiral aryl‐substituted allenes undergo facile cyclodimerization under neat conditions at 25 °C, in contrast to an earlier report that cyclodimerization takes place at 80 °C in benzene, which further illustrates the importance of the two‐step procedure reported herein because the chiral propargylamine may be converted into chiral allene when required.

An organobase‐controlled, divergent cascade reaction to construct spirocyclohexene indane‐1,3‐diones and coumarin‐fused cyclopentanes is reported. The cascade reaction is triggered by the 1,6‐addition of 3‐homoacylcoumarins to the indanedione‐derived acceptors and further regio/chemoselective reaction that preferentially resulted in spiro systems and fused cyclopentanes in a diversity‐oriented manner. The 1,6‐addition/aldol and 1,6‐addition/vinylogous Michael addition cascade processes were controlled by different base/solvent systems to the predominant formation of one of the two carbocyclic compounds.magnified image

The bifunctional quinine-catalyzed stepwise (3 + 2) cycloaddition for the enantioselective construction of spirooxindole-fused cyclopenta[c] chromen-4-ones is developed. The reactions of 3homoacylcoumarins and alkylidene oxindole electrophiles generate aforementioned spirooxindolechromenone adducts bearing five contiguous stereocenters, of which one is the spiro all-carbon quaternary stereocenter in high yields (up to 99%) with excellent stereoselectivities (up to > 20:1 dr and 99% ee). This methodology was investigated for three different alkylidene oxindole electrophiles and could also be practically demonstrated on a gram scale. Mechanistic investigations revealed that the (3 + 2) cycloaddition for the enantioselective synthesis of spirooxindole-fused cyclopenta[c]chromen-4-ones is proceeding via a stepwise reaction pathway.