Asymmetric Ring-Opening Reactions of Aza- and Oxa-bicyclic Alkenes with Boronic Acids Using a Palladium/Zinc Co-catalytic System

Ruthenium-catalyzed C-H functionalization of indoles and indolines with 7-azabenzonorbornadienes: access to aminodihydronaphthyl indoles and indolines

Indoles, indolines and hydronaphthylamines are ubiquitous structural motifs in natural products, pharmaceuticals, and biologically active molecules. In this paper, we report the synthesis of aminodihydronaphthyl-substituted indoles and indolines via a Ru-catalyzed carbamoyl-directed C-H functionalization of indoles and indolines with 7-azabenzonorbornadienes. In the presence of Cu(OAc)2 and AgSbF6, [Ru(p-cymene)Cl2]2 catalyzes the reaction of 1-carbamoylindoles with 7-azabenzonorbornadienes to produce 2-(1-amino-1,2-dihydronaphthalen-2-yl)indoles. Under the same conditions, the reaction of 1-carbamoylindolines with 7-azabenzonorbornadienes affords 7-(1-amino-1,2-dihydronaphthalen-2-yl)indolines. In both cases, the reactions yield cis-configured products.

Palladium-catalyzed stereocontrolled ring-opening of 7-oxabenzonorbornadienes with organic carboxylic acids

A palladium-catalyzed tandem reaction of 7-oxabenzonorbornadienes with organic carboxylic acids that provides cis-1,2-dihydro-l-naphthyl derivatives in moderate to good yields in a highly diastereoselective manner is described. A possible reaction mechanism involving syn acylation followed by insertion and diastereoselective ring-opening with 7-oxabenzonorbornadienes is proposed to account for the reaction.

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes

Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate, which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Upon substitution, different modes of reactivity arise, contributing to the possibility of multiple stereo-, regio-, and in extreme cases, constitutional isomers, which can provide unique means of constructing a variety of synthetically useful cyclic frameworks. To maximize selectivity, an understanding of bridgehead substituent effects is crucial. To that end, this review outlines hitherto reported examples of bridgehead substituent effects on the chemistry of unsymmetrical C1-substituted OBDs.

Catalytic asymmetric transformations of oxa- and azabicyclic alkenes

This review provides an overview of the fundamental concepts and recent developments in a wide range of enantioselective transformations involving oxa- and azabicyclic alkenes.

Ni-Catalyzed Iterative Alkyl Transfer from Nitrogen Enabled by the In Situ Methylation of Tertiary Amines

Current methods to achieve transition-metal-catalyzed alkyl carbon-nitrogen (C-N) bond cleavage require the preformation of ammonium, pyridinium, or sulfonamide derivatives from the corresponding alkyl amines. These activated substrates permit C-N bond cleavage, and their resultant intermediates can be intercepted to affect carbon-carbon bond-forming transforms. Here, we report the combination of in situ amine methylation and Ni-catalyzed benzalkyl C-N bond cleavage under reductive conditions. This method permits iterative alkyl group transfer from tertiary amines and demonstrates a deaminative strategy for the construction of Csp³-Csp³ bonds. We demonstrate PO(OMe)₃ (trimethylphosphate) to be a Ni-compatible methylation reagent for the in situ conversion of trialkyl amines into tetraalkylammonium salts. Single, double, and triple benzalkyl group transfers can all be achieved from the appropriately substituted tertiary amines. Transformations developed herein proceed via recurring events: the in situ methylation of tertiary amines by PO(OMe)₃, Ni-catalyzed C-N bond cleavage, and concurrent Csp³-Csp³ bond formation.

Intramolecular Palladium-Catalyzed Ring Opening of Oxabenzonorbornadienes with C1-Tethered Aryl Halides

The novel intramolecular ring opening of oxabenzonorbornadienes with C₁-tethered aryl halides was investigated using palladium catalysts to form fused tetracyclic frameworks. The reaction was generally found to synthesize 1,2-dihydronaphthalen-1-ol products with mild selectivity but was capable of synthesizing dehydrated naphthalene products in excellent yield and selectivity. Substituent effects on oxabenzonorbornadiene and on the iodoarene were explored along with the effects of varying tether length, where an efficient reaction was observed in nearly all cases. A total of 16 examples are reported with yields ranging from 0 to 96%.

Palladium-Catalyzed syn-Stereocontrolled Ring Opening of Oxabicyclic Alkenes with Arylsulfonyl Hydrazides

A novel palladium-catalyzed ring-opening reaction of oxabicyclic alkenes with arylsulfonyl hydrazides was first developed. In this work, we provide an efficient one-pot reaction to afford the corresponding cis-2-aryl-1,2-dihydronaphthalen-1-ols and 2-aryl-naphthalenes in moderate to excellent yields (up to 95%) under an open-air condition. Various types of functional groups attached to the substrates were tolerated well in this method. Among them, the cis-1,2-configuration of product 3ag was confirmed by X-ray crystallographic analysis. In addition, a plausible mechanism for ring opening was also proposed.

Palladium/silver co-catalyzed syn-stereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with amides

The first syn-stereoselective generation of 1,2-diamino dihydronaphthalene derivatives by asymmetric ring-opening reaction of azabenzonorbornadienes is reported.

Desymmetrization of Achiral Heterobicyclic Alkenes through Catalytic Asymmetric Hydrophosphination

Asymmetric addition of diarylphosphines to oxa- and azabicyclic alkenes proceeded in the presence of a chiral phosphapalladacycle catalyst and a mild acid at room temperature to give exclusively the enantioenriched addition products in excellent yields and good selectivities. Three new chiral carbon centers were generated stereoselectively by the catalytic hydrophosphination reaction.

Nickel-Catalyzed Asymmetric [2+2] Cycloaddition Reaction of Hetero-Bicyclic Alkenes with Internal Alkynes

Enantioselective [2+2] cycloaddition reaction of azabenzonorbornadienes and oxabenzonorbornadienes with internal alkynes has been enabled by a catalyst system comprising Ni(COD)₂ and (R)-SIPHOS-Ph-Mor. This transformation represents the first asymmetric [2+2] cycloaddition reaction of azabenzonorbornadienes with internal alkynes, providing a straightforward method to prepare four-membered carbocycles.

Cobalt-catalyzed asymmetric reactions of heterobicyclic alkenes with in situ generated organozinc halides

A general strategy for the asymmetric allylation and benzylation of heterobicyclic alkenes is described by employing in situ generated organozinc halides.

Platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with sodium arylsulfinates

A new efficient platinum-catalyzed ring-opening reaction of oxabicyclic alkenes with a wide range of sodium arylsulfinates was developed.