Rhodium(III)‐Catalyzed, CH Activated Annulation to Form Isocoumarins and α‐Pyrones using the ON Bond as an Internal Oxidant

Abstract

A mild, efficient and regioselective CH activation‐based intermolecular redox‐neutral annulation of O‐benzoylhydroxylamines and internal alkynes has been achieved. The protocol employs an ON bond as the internal oxidant and leads to isocoumarins and α‐pyrones.

The CH Activation/1,3‐Diyne Strategy: Highly Selective Direct Synthesis of Diverse Bisheterocycles by RhIII Catalysis

“…[16] Using the readily prepared product 6 a, we then demonstrated multiple annulation with many kinds of substrates (Scheme 4). [17][18][19][20][21] As expected, benzamides with a functional group (1 b) or heteroarene (1 c) reacted smoothly with 6 a to generate nonsymmetrical bisisoquinolones 3 in good yields and excellent selectivity. By using this stepwise approach, we also demonstrated the formation of other kinds of heterocycles, including isoquinolines, [17] pyrroles, [18] a-pyrones, [19] and benzoxepines, [20] as the second core structure (Scheme 4).…”

“…Apart from the synthetic achievements, the inherent selectivity of 1,3-diynes in the migratory insertion also attracted our attention (see also the Supporting Information). Although the selectivity of aryl alkyl alkynes and alkenyl alkyl alkynes has been well investigated, [12][13][14][17][18][19][20][21] the selectivity between the substituents of alkynes, such as alkynyl, isoquinolonyl, phenyl, and alkyl groups, has not been studied in C À H activation. [8] Based on our observations, the regioselectivity of the migratory insertion in this study is highly affected by the hybridization of the carbon atom and the coordinative ability of the substituents, with the order of preference being alkynyl and isoquinolonyl, phenyl, and .…”

Die C‐H‐Aktivierungs/1,3‐Diin‐Strategie: hochselektive direkte Synthese vielfältiger Bisheterocyclen mithilfe von RhIII‐Katalyse

“…Zuschriften tivität der Arylalkylalkine und Alkenylalkylalkine bereits untersucht wurde, [12][13][14][15][16][17][18][19][20][21] . Stichwçrter: Alkine · C-H-Aktivierung · Heterocyclen · Rh III -Katalyse · Selektivität…”

“…[16] Mithilfe des leicht zugänglichen Produktes 6 a demonstrierten wir die Zweitanellierungen mit einigen anderen Substraten (Schema 4). [17][18][19][20][21] Wie erwartet reagierten funktionalisierte (1 b) und heterocyclische Benzamide (1 c) glatt mit 6 a zu unsymmetrischen Bisisochinolonen 3 in guten Ausbeuten und mit exzellenten Selektivitäten. Mit diesem schrittweisen Prozedere demonstrierten wir ebenso die Synthese anderer Arten von Heterocyclen als zweiter Kernstruktur (Schema 4), unter anderem Isochinoline, [17] Pyrrole, [18] a-Pyrone [19] und Benzoxepine.…”

RhIII‐Catalyzed Regioselective Preparation of 3‐Hetero‐Substituted Isocoumarins from Aryl Carboxylic Acids and Alkynes

“…Phthalides and naphthalenes, however, were obtained as byproducts because of the low regioselectivity of the process or the lack of catalytic efficiency. Recently, various reports of N–O or O–O bonds as internal oxidants or the use of other external oxidants have improved the diversity of theses transformations towards the synthesis of pivotal molecules. Although alkynyl phosphonates have been successfully applied to the construction of hetero‐ and carbocyclic compounds, there are few reports of the synthesis of P‐ or N‐substituted isocoumarins from alkynyl phosphonates by a direct C–H bond activation pathway using oxygen as a clean oxidant.…”