Synthesis of Spirooxindole‐Benzo[d]oxazoles and Dihydrobenzofurans through Cycloaddition and Rearrangement of N‐Vinyl Nitrones and Arynes

Abstract

Various spirooxindole‐benzo[d]oxazoles and dihydrobenzofurans were prepared in good to excellent yields by [3+2] cycloaddition and selective rearrangement of N‐vinyl oxindole nitrones and arynes under transition metal‐free conditions. Experimental results showed that the substituent on the nitrone N‐vinyl group controlled the [1,3]‐ or [3,3]‐rearrangement of their cycloadduct owing to its steric effect. The present method features broad substrate scope, good functional group tolerance, controllable [1,3]‐ or [3,3]‐rearrangement, and diverse oxindole scaffolds.

Advances in the synthesis of nitrogen-containing heterocyclic compounds byin situbenzyne cycloaddition

“…This cascade reaction is a new pathway in the synthesis of nitrogen-containing heterocyclic compounds via prepared by [3 + 2] cycloaddition and selective rearrangement of N-vinyl oxindole nitro compounds and benzynes compounds under transition-metal-free conditions in good to excellent yields (Scheme 17b). 81 Zhang et al developed a [3 + 2] cyclization/arylation of isatin N,N ′ -cyclic azomethine imine 1,3dipole with in situ generated benzyne to access 3,3-disubstituted oxindole scaffolds in moderate yields. The method could form various biologically active disubstituted oxindoles with simple and mild reaction advantages, practical and one-pot (Scheme 17c).…”

Nitronate-aryne cycloaddition as a concise route to stereochemically complex fused benzisoxazolines and amino alcohols

“…Indeed, this reaction is expected to afford benzene-fuzed nitrosoacetals 5 or 6 , which may serve as precursors of aminoalcohols 7 and 8 bearing a phenol moiety. Albeit cycloadditions of arynes with various N -oxide-based 1,3-dipoles (nitrones, 10 nitrile oxides, 11 heterocyclic N -oxides 12 ) have been extensively studied in recent years, nitronates remain unexplored in these reactions. In our recent communication, 13 we reported that the reaction of C(3) unsubstituted 5,6-dihydro-4 H -1,2-oxazine N -oxides 1 (R = H) with Kobayashi's aryne precursors 14 9 produced 3-(2-hydroxyaryl)-substituted 1,2-oxazines 10 , which were likely formed by a spontaneous fragmentation of the five-membered ring in the initially generated cycloadducts 5 .…”

Photocatalytic Dearomative Intermolecular Seven‐Membered Ring Construction of Benzofurans

“…Intramolecular reactions include phenolic cyclization, [7] Claisen/cyclization sequence, [8] reductive Heck coupling, [9] and sigmatropic rearrangement [5e,10,11] . For intermolecular reactions, addition/cyclization, [12,13] oxidative coupling, [14] and cyclization/rearrangement sequence have been used [15] . Dearomative annulation using benzofuran as a substrate is one of the simplest strategies.…”