Insertion of N-Tosylacetimidates/Acetimidamides onto Arynes via [2 + 2] Cycloaddition

Abstract

A novel insertion reaction of N-tosylacetimidates and N-tosylacetimidamides onto arynes via a benzocyclobutene intermediate followed by ring cleavage is developed to afford o-benzylbenzoic acid derivatives in good yields. Interestingly, the use of cyclic 2-sulfonyliminoindolines provided two distinct products such as azepanimines via [2 + 2] cycloaddition and indolamines via protonation based on solvent medium.

Syntheses of 2-Aroyl Benzofurans through Cascade Annulation on Arynes

“…We have recently taken advantage of Stolz’s contributions in benzyne chemistry for the total synthesis of natural products . Also, we were successful in adding imidate functionality to benzynes to generate disubstituted aryl systems with minimal effort . We were exploring to develop a strategy for easy entry to 2-substituted benzofurans enroute the total synthesis of natural products and bioactive molecules (Figure ).…”

“…7 Also, we were successful in adding imidate functionality to benzynes to generate disubstituted aryl systems with minimal effort. 8 We were exploring to develop a strategy for easy entry to 2-substituted benzofurans enroute the total synthesis of natural products and bioactive molecules (Figure 1). 9 In 2017, Miyabe et al have recently reported the synthesis of dihydrobenzofurans and benzofurans from arynes, wherein o-QM reacts with diethyl 2-chloromalonate and diethylzinc at −40 to −60 °C in DMF as a solvent.…”

Recent Advances in Benzocyclobutene Chemistry

“…Interestingly, the same reaction was realized with cyclic 2sulfonyliminoindolines 319 affords the two different products such as azepanimines 321 through [2 + 2] cycloaddition and indolamines 322 through protonation (Scheme 51). [105] Ramtohul and Blackburn have reported a mild approach to the preparation of N-substituted α,α-disubstituted benzocyclobutene amino ester and isoquinoline 3-carboxylates using benzyne chemistry. The reaction of 2-amidoacrylate esters 323 with benzyne precursors 102 in the presence of CsF generated a mixture of substituted isoquinolines 325 as major products and α,α-disubstituted benzocyclobutenes 324 as minor products (Scheme 52).…”

Site-selective amination and/or nitrilationviametal-free C(sp2)–C(sp3) cleavage of benzylic and allylic alcohols

“…In recognition of increasingly strict conservational and regulatory imperatives, 1 much attention is now focused upon innovative functionalization methodologies 2 that are applicable to more readily available and economic feedstocks, 3 while simultaneously emphasizing environmentally friendly, especially metal-free, reaction conditions. 4 To these ends, there has been encouraging progress recently in the application of site-selective C(sp 2 )–C(sp 3 ) and C(sp 2 )–C(sp 2 ) cleavage strategies, 5 despite the comparatively high bond dissociation energy of most unstrained C–C bonds and the formidable challenges posed by discriminating amongst otherwise chemically equivalent C–C bonds 6 ( Fig. 1 ).…”