(3 + 2) Cycloaddition Reaction of the Endocyclic N-Silyl Enamine and N,N′-Cyclic Azomethine Imine

Abstract

We describe the (3 + 2) cycloaddition reaction of endocyclic N-silyl enamines and N,N′-cyclic azomethine imines. This process utilized the versatile endocyclic N-silyl enamine intermediates from the dearomative hydrosilylation of Nheteroarenes. The resulting tetracyclic pyrazolidinone structure was synthesized by a straightforward and atom-economical process. We also discussed the plausible origins of the different reactivity and endo/exo selectivity in terms of the structures of each proposed transition state. The successful gram-scale synthesis demonstrated the synthetic utility.

Oxidative (3+3) Cycloaddition/Ring-Opening Reactions of Simple Urea Derivatives and N,N′-Cyclic Azomethine Imines to Construct 1,2,3,5-Tetrazine-4(1H)-one Derivatives

“…Heterocyclic compounds are key structural units, − in particular, nitrogen-containing heterocycles are typical motifs, which are present in an array of bioactive natural products, drugs, and agricultural chemicals. − In the past two decades, the 1,3-dipolar cycloaddition reaction has become one of the most powerful methods for the rapid synthesis of nitrogen-containing heterocyclic compounds. − As an important type of 1,3-dipole, N , N ′-cyclic azomethine imines have been greatly applied in catalytic [3 + 2], [3 + 3], , [3 + 4], and [3 + 5] cycloaddition reactions toward the synthesis of corresponding five- to eight-membered nitrogen-containing rings. For example, in 2012, Kobayashi and co-workers developed Ag­(I)- or Cu­(I)-catalyzed 1,3-dipolar cycloadditions of N , N ′-cyclic azomethine imines with terminal alkynes, furnishing N , N -bicyclic pyrazolidinone derivatives .…”

“…Based on the above-mentioned (3 + n ) cycloadditions involving N , N ′-cyclic azomethine imines − and cycloaddition reactions about the in situ generated diaza-oxylallyl cations, − we designed an unreported (3 + 3) cycloaddition between N , N ′-cyclic azomethine imines and the in situ generated diaza-oxylallyl cations for the synthesis of pyrazolo­[1,2- a ]­[1,2,3,5]-tetrazine-2,8­(1 H )-dione derivatives, however, an unexpected (3 + 3) cycloaddition/ring-opening process was observed, leading to 1,2,3,5-tetrazine-4­(1 H )-one derivatives as main products, while the pyrazolo­[1,2- a ]­[1,2,3,5]-tetrazine-2,8­(1 H )-dione derivatives were not observed (Scheme d). Herein, we report our preliminary results of this (3 + 3) cycloaddition reaction.…”

Regioselective 1,2-Hydrosilylation of N-Heterocycles Catalyzed by a Ruthenium Olefin Metathesis Catalyst

“…Recently, the dearomatization of quinolines, via the use of excess borane and silane, has attracted attention. During this process, harsh reaction conditions are avoided and N-sila- or -bora-functionalized molecules can be used as key intermediates for further functionalization . Despite these recent significant advances in quinoline hydroboration and hydrosilylation, the latter methods are still far from general.…”

Organocatalytic alkylation and photoorganocatalyst-free acylation of azomethine imines by Hantzsch esters under blue LED light

“…8 Prior to these reports, while the azomethine imine class of molecules had been extensively utilised in 1,3-dipolar cycloaddition and nucleophilic addition reactions, their UV-mediated photoisomerisation and -cyclisation chemistry has received significantly less attention. 9,19,20 Building on these studies and as part of an ongoing programme dedicated to photocatalytic reaction development, we became interested in the potential reaction chemistry of azomethine imines with 4-alkyl- and 4-acyl-substituted-DHPs (Scheme 1f). 10 Our reaction design was guided by a number of synthetic protocols, as exemplified vide supra , exploiting the known propensity of DHPs to readily undergo heterolysis upon visible-light irradiation to give the carbon-centred radical species and their subsequent carbon–carbon bond formation reactions with an appropriately placed functional group.…”