Scandium(III)‐Triflate‐Catalyzed Pinacol‐Pinacolone Rearrangement and Cyclization of 1,2‐Diaryl‐1,2‐Ethanediol: A Versatile Synthesis of 1‐Aryl‐2,3‐Dihydro‐1H‐3‐Benzazepines

Abstract

An efficient scandium(III)-triflate-catalyzed pinacolpinacolone rearrangement and cyclization of 1,2-diaryl-1,2ethanediol has been developed, providing a variety of 2,3dihydro-1H-3-benzazepine derivatives in good yields. The obtained products could be transformed to other valuable building blocks for the synthesis of some biologically active compounds or natural products. Moreover, this protocol was also successfully employed for the synthesis of the corresponding 1-phenyl-3,4,5,6-tetrahydrobenzo[d]azocine and 3phenylisoquinoline products.

Advances and Perspectives in Pinacol Rearrangement Reactions: A Comprehensive Review

“…The knowledge gained from this study enhances our understanding of the photochemical processes involved in rearrangement reactions and expands the possibilities for the utilization of light in organic transformations. The study focuses on the development of an efficient and practical method to access these valuable compounds, highlighting the significance of pinacol rearrangement in this process [23]. The authors introduce the importance of 1-aryl-2,3-dihydro-1H-3-benzazepines as a class of organic compounds with potential pharmaceutical applications, due to their various biological activities.…”

4‐Aryl‐1H‐isochromenes Synthesis from Triol Derivatives through Brønsted Acid‐Catalyzed Pinacol Rearrangement/Intramolecular Cyclization Sequence

“…We recently investigated and reported the transition metal triflate-catalyzed pinacol rearrangement/intramolecular cyclization of substituted 1,2-diarylethanediol leading to the corresponding 5-aryl-2,3-dihydro-3benzazepine derivatives. [10] We anticipated that the triol 1 could similarly react with an acid and generate the secondary carbocation which would undergo a 1,2-aryl migration to form the aldehyde intermediate 2 followed by intramolecular cyclization of a primary alcohol moiety and dehydration to furnish the 4-aryl-1H-isochromene product 3 (Scheme 1e). [11,12] However, we also anticipated that a side reaction of triol 1 which could possibly generate the primary benzyl carbocation leading to polymerization of the substrate instead of the desired intramolecular cyclization at the late-stage of the reaction; this may be because the pinacol rearrangement reaction usually required some strong Lewis or Brønsted acids at high reaction temperature.…”

“…Hence, developing a new method to access the valuable 4‐substituted isochromene core structure still remains a challenge. We recently investigated and reported the transition metal triflate‐catalyzed pinacol rearrangement/intramolecular cyclization of substituted 1,2‐diarylethanediol leading to the corresponding 5‐aryl‐2,3‐dihydro‐3‐benzazepine derivatives [10] . We anticipated that the triol 1 could similarly react with an acid and generate the secondary carbocation which would undergo a 1,2‐aryl migration to form the aldehyde intermediate 2 followed by intramolecular cyclization of a primary alcohol moiety and dehydration to furnish the 4‐aryl‐1 H ‐isochromene product 3 (Scheme 1e) [11,12] .…”

Consecutive π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition promoted by in situ generated 2-benzopyrylium as the photoredox catalyst

“…The use of benzyltrimethylsilane derivatives 2 as the donor molecules 11 for the single-electron transfer (SET) to catalytically generated 2-benzopyrylium intermediates A under light irradiation results in the formation of radical cations B for further transformations. The nucleophilic nature of radicals C, which are generated by desilylation from corresponding radical cations B, facilitates radical addition to 2-benzopyrylium intermediates A, giving rise to corresponding 1 H -isochromene derivatives 3 12 through further reduction by SET from radical intermediates D. Meanwhile the SET oxidises D to regenerate 2-benzopyrylium intermediates A that function not only as electrophilic substrates but also as photoredox catalysts.…”