Transition‐Metal‐Catalyzed CH Bond Functionalizations: Feasible Access to a Diversity‐Oriented β‐Carboline Library

Diversification of the β‐carboline skeleton has been demonstrated to assemble a β‐carboline library starting from the tetrahydro‐β‐carboline framework. This strategy affords feasible access to heteroaryl‐, aryl‐, alkenyl‐, or alkynyl‐substituted β‐carbolines at the C1, C3, or C8 position through three categorically different types of transition‐metal‐catalyzed C?C bond‐forming reactions, in the presence of multiple potentially reactive positions. These site‐selective functionalizations include; 1) the Cu‐catalyzed C1/C3‐selective decarboxylative C?C and C?C_sp coupling of hexahydro‐β‐carboline‐3‐carboxylic acid with a C?H bond of a heteroarene or terminal alkyne; 2) the chelation‐assisted Pd‐catalyzed C1/C8‐selective C?H arylation of hexahydro‐β‐carboline with aryl boron reagents; and 3) the chelation‐assisted Pd‐catalyzed C1/C3‐selective oxidative C?H/C?H cross‐coupling of β‐carboline‐N‐oxide with arenes, heteroarenes, or alkenes. The saturated structural feature of the hexahydro‐β‐carboline framework can increase reactivity and control site selectivity. The robustness of these approaches has been demonstrated through the synthesis of hyrtioerectine analogues and perlolyrine. We believe that these strategies could provide inspiration for late‐stage diversifications of bioactive core scaffolds.     

Copper-catalyzed decarboxylative C−P cross coupling of arylpropiolic acids with dialkyl hydrazinylphosphonates leading to alkynylphosphonates

A facile and novel copper-catalyzed decarboxylative coupling of various arylpropiolic acids with readily available dialkyl hydrazinylphosphonates has been developed, providing an attractive synthetic tool for the synthesis of valuable alkynylphosphonates with operational simplicity and mild reaction conditions.     

Stereospecific Pd‐Catalyzed Intermolecular C(sp3)–C(sp) Cross‐Coupling of Diarylmethyl Carbonates and Terminal Alkynes Under Base‐Free Conditions

A palladium‐catalyzed intermolecular decarboxylative C(sp³)–C(sp) coupling of diarylmethyl carbonates and terminal alkynes has been developed. The reaction proceeds smoothly under external base‐free conditions to deliver the corresponding alkynylated diarylmethanes with the liberation of CO₂ and MeOH as the sole byproducts. Moreover, enantioenriched diarylmethyl carbonates are stereospecifically converted to optically active cross‐coupling products with inversion of configuration. Thus, the stereospecific palladium catalysis can provide new and unique access to the alkynylated chiral tertiary stereocenters, which are relatively difficult to construct by conventional methods.     

Iron‐Catalyzed Decarboxylation of Trifluoroacetate and Its Application to the Synthesis of Trifluoromethyl Thioethers

Nucleophilic CF₃ has been generated by decarboxylation of potassium trifluoroacetate, arguably the most easy‐to‐handle, inexpensive, and sustainable source of trifluoromethyl groups. Simple iron(II) chloride catalyzes the decarboxylation as well as a subsequent trifluoromethylation of organothiocyanates, resulting in a straightforward synthesis of trifluoromethyl thioethers. The KCN byproduct is absorbed by iron(II) with formation of nontoxic potassium hexacyanoferrate. An analogous trifluoromethylation of aldehydes with trifluoroacetate underlines the synthetic potential of such iron‐catalyzed decarboxylative trifluoromethylations.     

Short and Divergent Total Synthesis of (+)‐Machaeriol B, (+)‐Machaeriol D, (+)‐Δ8‐THC,and Analogues

Short and highly efficient stereoselective syntheses provide machaeriols and cannabinoids in a divergent approach starting from a common precursor, commercially available (S)‐perillic acid. Key features of the novel strategy are a stereospecific palladium‐catalyzed decarboxylative arylation and a one‐pot sequence comprising a stereoselective hydroboration followed by oxidation or reduction of the corresponding intermediary boranes. The divergent approach is convincingly demonstrated by the five‐step syntheses of (+)‐machaeriol B, (+)‐machaeriol D, and related analogues, and the four‐step synthesis of (+)‐Δ⁸‐THC and an analogue.     

Electrochemical decarboxylative sulfonylation of arylacetylenic acids with sodium arylsulfinates: Access to arylacetylenic sulfones

Abstract

An efficient decarboxylative sulfonylation of arylacetylenic acids with sodium arylsulfinates has been achieved by an electro-oxidative strategy. This novel protocol offers a simple, efficient, and green route to a series of arylacetylenic sulfones in moderate yields under metal-free and external oxidant-free conditions.     

A new synthesis of A-nor△3(5), 9 (10) -estradiene-2,17-dione

A-nor-△³⁽⁵⁾’⁹⁽¹⁰⁾-estradiene-2, 17-dione 1, a potential precursor for synthesis of some new steroidal contraceptlves, was synthesized from 3Phydroxy-5a-chloro-6ß, 19-epoxy-androstane-17-one 6 as the starting rnateri-al, which is the key intermediate of steroidal contraceptive of norethindrone, in an overall yield of 25 % in 5 steps through the sequence of 5 reactions: (i) oxidative decyclization. (ii) decarboxylative cyclization, (iii) reductive decy-clization, (iv) dehydroxy methylation, (v) deacetoxylation.     

Electrophotochemical Metal-Catalyzed Decarboxylative Coupling of Aliphatic Carboxylic Acids

An electrophotochemical dual metal-catalyzed protocol for decarboxylative arylation of simple aliphatic carboxylic acids with aryl halides is reported. The relative stabilities of catalytically active metal complexes simultaneously generated at anode and cathode are the key design elements for the success of this convergent paired electrolysis. This new electrophotocatalytic method is mild, robust, and most importantly, capable of accommodating simple primary aliphatic acids including acetic acid – ubiquitous and variegated structural motifs yet remain oddly challenging substrates – directly as native functional groups for decarboxylative C(sp²)−C(sp³) bond formation.     

Ligand‐free Pd/Cu‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates

This paper describes a palladium/copper‐catalyzed decarboxylative coupling of aryl iodides with α‐oxocarboxylates. The cross‐coupling reaction gives high chemical yields of aryl ketones and has wide functional group tolerance, making the transformation an attractive alternative to the traditional cross‐coupling approaches for aryl ketones. Copyright © 2014 John Wiley & Sons, Ltd.