Dearomatization of 3-Nitroindoles Enabled Using Palladium-Catalyzed Decarboxylative [4 + 2] Cycloaddition of 2-Alkylidenetrimethylene Carbonates

Abstract

A dearomatization process of 3-nitroindoles enabled using palladium-catalyzed decarboxylative [4 + 2] cycloaddition of either 2-alkylidenetrimethylene carbonates or 2-(hydroxymethyl)-3-arylallyl carbonates has been developed, affording a wide range of indoline-fused tetrahydropyrans in good yields with excellent diastereoselectivities. This reaction features a wide substrate scope and mild conditions and represents the first example of the application of π-allyl palladium 1,4-[O,C]-dipole species for the dearomative cycloaddition of electron-deficient heteroarenes.

Pd-catalyzed oxa-[4 + n] dipolar cycloaddition using 1,4-O/C dipole synthons for the synthesis of O-heterocycles

“…A dearomatization process via Pd-catalyzed diastereoselective oxa-[4 + 2] dipolar cycloadditions of ADTMCs 1 or 2-hydroxymethylallyl carbonates 2 with 3-nitroindoles 29 as electron-deficient heteroarenes was developed by the Zhao and Yuan group (Scheme 9). 19 These dearomative cycloadditions yielded indole-fused tetrahydropyrans 30 and 31 with excellent diastereoselectivities. In the catalytic system of Pd(0) and PPh 3 in acetonitrile, substituted 2-nitroindoles 29 were well tolerated in the reaction with ADTMC 1 .…”

Transition‐Metal Catalyzed [4+2]‐Cycloaddition Reactions: A Sexennial Update

“…Palladium catalyzed synthesis of indoline-fused tetrahydropyrans. [99] (2-pyridyl)ketimines 103 instead of 2-aminopyridine and carbonyl compound. Interestingly, [4 + 2] cycloaddition of 103 and terminal alkynes 104 furnished 2H-pyrido[1,2-a]pyrimidines 105 elegantly via 6-endo-dig-cyclization (Scheme 28).…”

Diverse Synthesis of Fused Polyheterocyclic Compounds via [3 + 2] Cycloaddition of In Situ-Generated Heteroaromatic N-Ylides and Electron-Deficient Olefins

“…In this context, given the importance of N,S-polyheterocyclic scaffolds in medicinal and natural product chemistry and the great potential of the benzothiazolium salts for cycloaddition, expanding the application of benzothiazolium salts in the reaction with different type of electron-deficient olefins for the [3 + 2] cycloaddition to access structurally diverse polyheterocyclic compounds is highly desired. Therefore, based on our unremitting efforts in developing new synthetic methods for the construction of structurally diverse heterocyclic compounds [57][58][59][60][61], the [3 + 2] cycloaddition reactions of benzothiazolium salts and diverse electron-deficient olefins including maleimides, 3-trifluoroethylidene oxindoles, and benzylidenemalononitriles have been realized, furnishing varieties of functionalized fused polyheterocyclic compounds (Scheme 1, bottom). Herein, we hope to report the results of our study.…”