Divergent Asymmetric Synthesis of Polycyclic Compounds via Vinyl Triazenes

Abstract

Vinyl triazenes were obtained by enantioselective [2+ +2] cycloaddition reactions of bicyclic alkenes with 1-alkynyl triazenesi nt he presence of aR u II catalyst with ac hiral cyclopentadienyl ligand. These triazenes serve as unique vinyl cation surrogates.U nder acidic conditions,t he triazene functionality can be replaced with avariety of groups, including halides,a lkoxides,s ulfoxides,a mides,a renes,a nd heteroarenes,thus providing efficient access to apool of chiral polycyclic compounds.

Gold‐Catalyzed Synthesis of 1,3‐Diaminopyrazoles from 1‐Alkynyltriazenes and Imines

“…From a more general point of view, our results are further evidence for the synthetic utility of 1‐alkynyltriazenes. So far, we have stressed that 1‐alkynyltriazenes are activated alkynes with a reactivity profile similar to ynamides . The present results show that the triazene function can participate directly in chemical transformations via C–N coupling reactions.…”

Gold-Catalyzed Synthesis of Small Rings

“… 690 , 692 , 695 This becomes particularly challenging when alkynes 719 are used in place of allenes. 720 , 721 This approach has been developed using Co, 722 Zn, 723 Ni, 724 Cu, 725 − 729 Ru, 730 − 733 Rh, 734 Pd, 735 and Ir 736 , 737 catalysts using either cyclic alkenes or alkenes substituted with electron-withdrawing groups. In this context, Echavarren and co-workers reported the enanatioselective gold(I)-catalyzed synthesis of cyclobutenes by [2 + 2] cycloaddition between alkynes and alkenes using non- C 2 symmetric Josiphos chiral ligands ( Scheme 154 ).…”

Applications of Chiral Cyclopentadienyl (Cpx) Metal Complexes in Asymmetric Catalysis

“…The importance of the counterion was apparent later when the group used chiral Ru(II)Cp x complex 127 with a – PF 6 counterion for the [2+2] cycloaddition between bicyclic alkenes 126 and alkynes giving access to strained cyclobutenes 128 (Scheme 26). [ 67a ] Interestingly, increased enantioselectivity was achieved due to the binding of chloride anions (additive) to ruthenium to form a neutral, highly enantioselective, catalytic species.…”

“…soon after published a similar enantioselective Ru‐catalysed [2+2] cycloaddition using alkynyl triazenes as coupling partners. [ 67b ] The same complex 127 delivered high yields and enantioselectivities for a broad range of cyclobutenyl‐triazenes 129 (Scheme 26). Once again, the catalytic activity was enhanced by coordination of the halide anion additive to the metal centre.…”