Regioselective [3 + 2] Cycloaddition Reaction of 3-Alkynoates with Seyferth–Gilbert Reagent

Abstract

A Et 3 N-triggered regioselective [3 + 2] cycloaddition reaction of 3-alkynoates with Seyferth−Gilbert reagent has been developed to furnish a series of trisubstituted pyrazole-3phosphonates. A one-pot cycloaddition/alkylation sequence further offered access to the corresponding fully substituted pyrazoles.

La(OTf)3-Catalyzed [3+2] Cycloaddition Reactions for the Synthesis of Benzo[d]oxazoles/Benzofurans

“…One-step [3+2] cycloaddition (1,3-dipolar cycloaddition) is a straightforward synthetic strategy for the assembly of five-membered heterocyclic molecules, which is widely used in biologically and pharmaceutically important natural products, for example, the classic click reaction: [3+2]-dipolar cycloaddition of azides and alkynes to synthesize triazole derivatives; the [3 + 2]-cycloaddition reactions to construct pyrazolines and pyrazoles; polyoxygenated polycyclic spirolactones; pyrroles; bicyclic pyrrolidines; 5-CF 3 -1,3,4-oxadiazoles, etc …”

Silver-catalysed [3 + 2] annulation reaction of aryldiazonium salts with allenes enabled by boronate direction

“…12 The realization of this transformation would further expand the utility of both aryldiazonium salts and allenes in heterocycle synthesis. 13 Herein, we documented that N 1 -aryl-1 H -pyrazoles were constructed by the direct exploitation of a variety of aryldiazonium salts in the silver-catalysed [3 + 2] annulation reaction of allenylboronates (Scheme 1c). In this context, the boronate moiety could function as a traceless activating and directing group to facilitate regioselective allene incorporation, as supported by combined experimental and computational mechanistic studies.…”

Tandem Isomerization/α,β-Site-Selective and Enantioselective Addition Reactions of N-(3-Butynoyl)-3,5-dimethylpyrazole Induced by Chiral π–Cu(II) Catalysts

“…Among their many applications in chemistry, cycloaddition reactions of activated allenes represent a powerful strategy for the synthesis of a variety of carbocycles and heterocycles. , More importantly, asymmetric versions have been developed that greatly broaden their applications to include the synthesis of bioactive compounds. In recent years, 3-alkynoates have been explored as activated γ-substituted allenes in asymmetric cycloaddition reactions. − For example, in 2010, Loh’s group developed the tandem isomerization of 3-alkynoates to allenoates/α,γ-site-selective and enantioselective [3 + 2] cycloaddition via vinylphosphonium dipolar intermediates using chiral phosphine catalyst (Scheme a). In contrast, in 2009, Huang, Tan et al developed a tandem chiral guanidine-catalyzed enantioselective isomerization of 3-alkynoates to chiral allenoates/α,β-site-selective and diastereoselective [4 + 2] cycloaddition (Scheme b) .…”