Cinchonidine-Catalyzed Synthesis of Oxazabicyclo[4.2.1]nonanones from N-Aryl-α,β-unsaturated Nitrones and 1-Ethynylnaphthalen-2-ols

Abstract

A variety of oxazabicyclo[4.2.1]­nonanone derivatives were prepared in good yields through a cinchonidine-catalyzed cascade reaction of N-aryl-α,β-unsaturated nitrones and 1-ethynylnaphthalen-2-ols. Mechanistic studies show that the reaction undergoes a [4 + 3] cycloaddition of nitrones to vinylidene o-quinone methide generated in situ from 1-ethynylnaphthalen-2-ols in the presence of cinchonidine, 1,3-rearrangement of N–O vinyl moieties, ring-opening, and finally double intramolecular cyclizations to afford oxazabicyclo[4.2.1]­nonanones over five steps in a one-pot reaction.

Synthesis of Functionalized 2‐Pyrrolidinones Bearing N‐Trifluoromethylphenyl through A Formal [4+1] Cycloaddition of Cinnamaldehyde Nitrones and 1‐Ethynylnaphthalen‐2‐ols

“…Based on the above experimental results and previous work, [15] a possible mechanism for the formation of 3 aa / 4 aa from 1 a and 2 a was proposed (Scheme 3). Compound 2 a was activated by DABCO to afford vinylidene ortho ‐quinone methide A , which cyclized with nitrone 1 a to give intermediate B .…”

“…However, N-aryl nitrones with other substituent, such as phenyl (1 o), 4-OMe (1 p), 4-F (1 q), did not give any desired 2-pyrrolidinones under the optimized reaction conditions. In these three cases, the corresponding oxazabicyclo[4.2.1]nonanones reported in our previous work [15] were obtained only.…”

“…On the other hand, 1‐ethynylnaphthalen‐2‐ols have been extensively served as useful organic building blocks in organic synthesis owing to their easy transformation to vinylidene ortho ‐quinone methide [14] . In 2022, our group developed a new cascade reaction of N ‐aryl‐ α , β ‐unsaturated nitrones with 1‐ethynylnaphthalen‐2‐ols to prepare various oxazabicyclo[4.2.1]nonanones in good yields in the presence of cinchonidine catalyst and showed a distinct [1,3]‐rearrangement of N−O bond [15] . The prepared oxazabicyclo[4.2.1]nonanone could be converted to 2‐pyrrolidinone in the presence of m ‐CPBA (Scheme 1‐C).…”

“…[14] In 2022, our group developed a new cascade reaction of N-aryl-α,βunsaturated nitrones with 1-ethynylnaphthalen-2-ols to prepare various oxazabicyclo[4.2.1]nonanones in good yields in the presence of cinchonidine catalyst and showed a distinct [1,3]-rearrangement of NÀ O bond. [15] The prepared oxazabicyclo[4.2.1]nonanone could be converted to 2-pyrrolidinone in the presence of m-CPBA (Scheme 1-C). However, only one example was reported in the presence of m-CPBA.…”

Copper(II)‐Catalyzed Cascade Reactions of N‐Aryl Nitrones and Disubstituted Allenoates to Prepare [1,3]Oxazino[3,2‐a]indolines and Dihydropyrido[1,2‐a]indolines

“…The control of regioselective cyclization after [3,3]-rearrangement, diastereoselectivity of indoline products, and scaffold diversity of indolines are still challenging. Continuing to explore the reactivity of substituted allenoates as well as the cycloaddition of α,β-unsatu-rated nitrones in our group, [12] we surmised that the reaction of N-aryl-α,β-unsaturated nitrones and disubstituted allenoates would afford azepinone intermediates through [3 + 2] cycloaddition and [3,3]-rearrangement; the azepinones would be activated and controlled by catalyst to undergo further selective transformations (Scheme 1-C). The type of catalysts might control the activation mode and lead Ocyclization or C-cyclization of azepinone intermediate to access the diversity of indoline scaffolds.…”