Solvent‐Dependent Asymmetric Synthesis of Alkynyl and Monofluoroalkenyl Isoindolinones by CpRhIII‐Catalyzed C−H Activation

The asymmetric synthesis of alkynyl and monofluoroalkenyl isoindolinones from N‐methoxy benzamides and α,α‐difluoromethylene alkynes is enabled by C?H activation with a chiral CpRh^III catalyst. Remarkably, product formation is solvent‐dependent; alkynyl isoindolinones are afforded in MeOH (up to 86 % yield, 99.6 % ee) whereas monofluoroalkenyl isoindolinones are generated in ⁱPrCN (up to 98:2 Z/E, 93 % yield, 86 % ee). Mechanistic studies revealed chiral allene and E‐configured alkenyl rhodium species as reaction intermediates. The latter is transformed into the corresponding Z‐configured monofluoroalkene upon protonation in the ⁱPrCN system and into an alkyne by an unusual anti β‐F elimination in the MeOH system. Notably, kinetic resolution processes occur in this reaction. Despite the moderate enantiocontrol for the formation of the chiral allene, the Z‐monofluoroalkenyl isoindolinones and alkynyl isoindolinones were obtained in good enantiopurities by one or two sequential kinetic resolution processes.     

Catalytic Asymmetric Synthesis of Isoindolinones

As important reactive species, isoindolinones represent a cluster of valuable building blocks for the construction of natural‐product‐like compounds. In particular, chiral isoindolinones are the key structural feature of naturally occurring bioactive molecules. During the past decade, great advances have been made in the asymmetric synthesis of isoindolinone skeleton compounds. Hence, recent progress in catalytic asymmetric synthesis of isoindolinones is reviewed here, with emphasis on chiral organocatalysis and transition metal complexes enabled transformations. Different organocatalysts (chiral phosphoric acids, phase transfer catalysts, chiral thioureas) and chiral transition‐metal complexes (Rh, Pd, Ir, Cu, Mg, and Ni) are included in this transformation.     

Multicomponent Synthesis of Isoindolinone Frameworks via RhIII‐Catalysed in situ Directing Group‐Assisted Tandem Oxidative Olefination/Michael Addition

A Rh^III‐catalysed three‐component synthesis of isoindolinone frameworks via direct assembly of benzoyl chlorides, o‐aminophenols and activated alkenes has been developed. The process involves in situ generation of o‐aminophenol (OAP)‐based bidentate directing group (DG), Rh^III‐catalysed tandem ortho C?H olefination and subsequent cyclization via aza‐Michael addition. This protocol exhibits good chemoselectivity and functional group tolerance. Computational studies showed that the presence of hydroxyl group on the N‐aryl ring could enhance the chemoselectivity of the reaction.     

Synthesis of 3-Methyleneisoindolin-1-ones and Isoquinolinium Salts via Exo and Endo Selective Cyclization of 2-(1-Alkynyl)benzaldimines

Coinage metal-promoted 5-exo and 6-endo selective cyclization of 2-(1-alkynyl)benzaldimines has been studied. It was found that, under gold catalysis, 2-(1-alkynyl)benzaldimines exclusively underwent 5-exo-dig cyclization processes, followed by oxidation to form N-aryl 3-methyleneisoindolin-1-ones. In contrast, in the presence of base and under activation of AgOTf, switching of 5-exo to 6-endo cyclizations of 2-(1-alkynyl)benzaldimines was observed, exclusively giving N-aryl or N-alkyl substituted isoquinolinium salts. The two key reaction intermediates, exocyclic vinyl-Au and the endocyclic vinyl-Ag species have been isolated and characterized, and a study of their reactivities confirms the plausible mechanisms. Reactions of the resultant 3-methyleneisoindolin-1-ones with benzyne afforded structurally important isoindolinone-based benzocyclobutenes. Additionally, several interesting transformations of the resultant isoquinolinium salts have been investigated.     

Asymmetric Alkynylation/Lactamization Cascade: An Expeditious Entry to Enantiomerically Enriched Isoindolinones

An unprecedented Cu^I–pybox‐diPh‐catalyzed highly enantioselective (up to >99 % ee) alkynylation/lactamization cascade has been developed as a general catalytic system for the synthesis of diversely substituted isoindolinones of immense biological importance. The cascade effects one C? C and two C? N bond‐forming events in one reaction vessel under operationally simple, additive‐free reaction conditions in good to excellent yields. The methodology was further extended to the synthesis of tetrahydroisoquinoline scaffolds common to several biologically active natural products in a two‐step sequence with remarkable selectivity (up to 94 % ee).     

An asymmetric aerobic aza-wacker-type cyclization: synthesis of isoindolinones bearing tetrasubstituted carbon stereocenters

It's all in the solvent: An enantioselective variant of an aza-Wacker-type cyclization that gives isoindolinones containing tetrasubstituted carbon centers α to the nitrogen atom has been developed (see scheme; tfa=trifluoroacetate). The use of a highly coordinating solvent is crucial for the activity of the catalyst and the stereoselectivity the reaction (up to 99?%?ee).     

Unexpected cyclization route for o-ethynylbenzoic acids hydrazides in the presence of base

The reaction of o-ethynylbenzoic acids hydrazides with base has been studied. In the presence of a strong donor substituent (1,5-dimethylpyrazol-4-yl) it has been found that an unusual cyclization route occurs to give the corresponding benzopyridazinone instead of the expected isoindolinone. Dedicated to Academician B. A. Trofimov in his 70^th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 67-70, January, 2009.     

Palladium‐Catalyzed Carbonylation of 2‐Bromoanilines with 2‐Formylbenzoic Acid and 2‐Halobenzaldehydes: Efficient Synthesis of Functionalized Isoindolinones

A concise and highly versatile method for the synthesis of functionalized isoindolinones is reported. Various 2‐bromoanilines undergo palladium‐catalyzed carbonylation with 2‐formylbenzoic acid under a convenient and mild procedure to give good to excellent yields of the corresponding isoindolinones. Additionally, 2‐halobenzaldehydes can be applied as substrates in palladium‐catalyzed double‐carbonylation to provide identical compounds in moderate to good yields.