(E)‐,(Z)‐Parallel Preparative Methods for Stereodefined β,β‐Diaryl‐ and α,β‐Diaryl‐α,β‐unsaturated Esters: Application to the Stereocomplementary Concise Synthesis of Zimelidine

Parallel and practical methods for the preparation of both (E)‐ and (Z)‐β‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 1 and (E)‐ and (Z)‐α‐aryl¹‐β‐aryl²‐α,β‐unsaturated esters 2 are described. These methods involve accessible, robust, stereocomplementary N‐methylimidazole (NMI)‐mediated enol tosylations (14 examples, 70–99 % yield), as well as stereoretentive Suzuki–Miyaura cross‐couplings (36 examples, 64–99 % yield). The highlighted feature of the present protocol is the use of parallel and stereocomplementary approaches to obtain highly (E)‐ and (Z)‐pure products 1 and 2 by utilizing sequential enol tosylations and cross‐coupling reactions. An expeditious and parallel synthesis of (E)‐ and (Z)‐zimelidine ( 3 ), which is a highly representative selective serotonin reuptake inhibitor (SSRI), was performed by utilizing the present methods.     

β,β‐Diborylated Subporphyrinato Boron(III) Complexes as Useful Synthetic Precursors

Iridium‐catalyzed borylation of B‐aryl meso‐free subporphyrinato boron(III) complexes (hereinafter referred to simply as subporphyrins) with bis(pinacolato)diboron gave 2,13‐diborylated subporphyrins regioselectively, which served as promising synthetic precursors for 2,13‐diarylated subporphyrins and doubly β‐to‐β 1,3‐butadiyne‐bridged subporphyrin dimers. 2,13‐Diarylated subporphyrins display perturbed absorption spectra, depending upon the β‐aryl substituents. Doubly 1,3‐butadiyne‐bridged syn and anti subporphyrin dimers thus prepared exhibit differently altered absorption spectra with split Soret‐like bands, which have been accounted for in terms of exciton coupling.     

Ligand‐free CuI‐catalyzed coupling and cyclization of β‐bromo‐α,β‐unsaturated amides with formamide leading to pyrimidinones

β‐Bromo‐α,β‐unsaturated amides were coupled and cyclized with formamide in DMF at 100°C in the presence of a catalytic amount of a copper(I) salt along with a base to give the corresponding pyrimidinones in good yields. Copyright © 2013 John Wiley & Sons, Ltd.     

α,α′‐Diarylacenaphtho[1,2‐c]phosphole P‐Oxides: Divergent Synthesis and Application to Cathode Buffer Layers in Organic Photovoltaics

A divergent method for the synthesis of α,α′‐diarylacenaphtho[1,2‐c]phosphole P‐oxides has been established; α,α′‐dibromoacenaphtho[c]phosphole P‐oxide, which was prepared through a Ti^II‐mediated cyclization of 1,8‐bis(trimethylsilylethynyl)naphthalene, underwent a Stille coupling with three different kinds of aryltributylstannanes to afford the α,α′‐diarylacenaphtho[c]phosphole P‐oxides in moderate to good yields. X‐ray crystallographic analyses and UV/Vis absorption/fluorescence measurements have revealed that the degree of π‐conjugation, the packing motif, the electron‐accepting ability, and the thermal stability of the acenaphtho[c]phosphole π‐systems are finely tunable with the α‐aryl substituents. All the P?O and P?S derivatives exhibited high stability in their electrochemically reduced state. To use this class of arene‐fused phosphole π‐systems as n‐type semiconducting materials, we evaluated device performances of the bulk heterojunction organic photovoltaics (OPV) that consist of poly(3‐hexylthiophene), an indene‐C₇₀ bisadduct, and a cathode buffer layer. The insertion of the diarylacenaphtho[c]phosphole P‐oxides as the buffer layer was found to improve the power conversion efficiency of the polymer‐based OPV devices.     

CuI/amino acid‐catalyzed coupling and cyclization of β‐bromo‐α,β‐unsaturated amides with terminal alkynes leading to (3Z)‐3‐alkylidenepyrrol‐1‐ones

β‐Bromo‐α,β‐unsaturated amides are coupled and cyclized with terminal alkynes in DMF at 110 °C in the presence of a catalytic amount of CuI and amino acid along with a base to give the corresponding (3Z)‐3‐alkylidenepyrrol‐1‐ones in moderate to good yields. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and Photophysical Properties of Doubly β‐to‐β Bridged Cyclic ZnII Porphyrin Arrays

A series of doubly β‐to‐β bridged cyclic Zn^II porphyrin arrays were prepared by a stepwise Suzuki–Miyaura coupling reaction of borylated Zn^II porphyrin with different bridge groups. The coupling of the building block of β,β′‐diboryl Zn^II porphyrin 1 with different bridges provided the doubly β‐to‐β carbazole‐bridged Zn^II porphyrin array 3 , the fluorene‐bridged Zn^II porphyrin array 5 , the fluorenone‐bridged Zn^II porphyrin array 7 , and the three‐carbazole‐bridged Zn^II porphyrin ring 8 . The structural assignment of 3 was confirmed by the X‐ray diffraction analysis, which revealed a highly symmetrical and remarkably bent syn‐form structure. The incorporation of bridge units with different electronic effects results in different photophysical properties of the cyclic Zn^II porphyrin arrays. Comprehensive photophysical studies demonstrate that the electron‐withdrawing bridge fluorenone has the largest electronic interaction with the Zn^II porphyrin unit among the series, thus resulting in the highest two‐photon absorption cross‐section values (σ⁽²⁾) of 6570±60 GM for 7 . The present work provides a new strategy for developing porphyrin‐based optical materials.     

Single‐Flask Multicomponent Palladium‐Catalyzed α,γ‐Coupling of Ketone Enolates: Facile Preparation of Complex Carbon Scaffolds

A three‐component palladium‐catalyzed reaction sequence has been developed in which γ‐substituted α,β‐unsaturated products are obtained in a single flask by an α‐alkenylation with either a subsequent γ‐alkenylation or γ‐arylation of a ketone enolate. Coupling of a variety of electronically and structurally different components was achieved in the presence of a Pd/Q‐Phos catalyst (2 mol %), usually at 22 °C with yields of up to 85 %. Most importantly, access to these products is obtained in one simple operation in place of employing multiple reactions.     

Indium Tribromide Catalyzed Coupling Reaction of Enol Ethers with Silyl Ketene Imines toward the Synthesis of β,γ‐Unsaturated Nitriles

Herein, a coupling reaction of enol ethers with silyl ketene imines in the presence of catalytic amounts of InBr₃ and Me₃SiBr is described. Kinetic studies have revealed that an indium catalyst and Me₃SiBr accelerated the coupling process and the regeneration of the catalyst, respectively. Various types of enol ethers and silyl ketene imines are applicable. In addition, a formal synthesis of verapamil was achieved by using this novel coupling reaction.     

Palladium‐catalyzed decarboxylative coupling of α,β‐unsaturated carboxylic acids with aryl tosylates

We report a general method for selective cross‐coupling of α,β‐unsaturated carboxylic acids with aryl tosylates enabled by versatile Pd(II) complexes. This method features the general cross‐coupling of ubiquitous α,β‐unsaturated carboxylic acids by decarboxylation. The transformation is characterized by its operational simplicity, the use of inexpensive, air‐stable Pd(II) catalysts, scalability and wide substrate scope. The reaction proceeds with high trans selectivity to furnish valuable (E)‐1,2‐diarylethenes.     

A Convenient Method for the Synthesis of α‐Ethynylphospholes and Modulation of Their π‐Conjugated Systems

Mind the (narrow) gap : α‐Ethynylphospholes generated in situ from the corresponding silyl‐capped precursors were converted into a series of α‐(arylethynyl) phospholes bearing functional substituents as well as an α,α′‐linked terphosphole (see scheme). The terphosphole has a narrow HOMO–LUMO gap owing to efficient π conjugation over the three phosphole rings.

     

Synthesis of α,α‐Difluoromethylene Alkynes by Palladium‐Catalyzed gem‐Difluoropropargylation of Aryl and Alkenyl Boron Reagents

gem‐Difluoropropargyl bromides are versatile intermediates in organic synthesis, but have rarely been employed in transition‐metal‐catalyzed cross‐coupling reactions. The first palladium‐catalyzed gem‐difluoropropargylation of organoboron reagents with gem‐difluoropropargyl bromides is now reported. The reaction proceeds under mild reaction conditions with high regioselectivity; it features a broad substrate scope and excellent functional‐group compatibility and thus provides an attractive approach for the synthesis of complex fluorinated molecules, in particular for drug discovery and development.     

Ligand‐Controlled α‐ and β‐Arylation of Acyclic N‐Boc Amines

The palladium‐catalyzed ligand‐controlled arylation of α‐zincated acyclic amines, obtained by directed α‐lithiation and transmetalation, is described. Whereas PtBu₃ gave rise to α‐arylated Boc‐protected amines, more flexible N‐phenylazole‐based phosphine ligands induced major β‐arylation through migrative cross‐coupling.     

CuI/amino acid catalysis in coupling and cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with terminal alkynes leading to alkylidenefuranones

β‐Bromo‐α,β‐unsaturated carboxylic acids are coupled and cyclized with terminal alkynes in DMF at 110°C in the presence of a catalytic amount of CuI and amino acid along with a base to give alkylidenefuranones in good yields. Similar reaction under microwave irradiation also gave alkylidenefuranones in higher yields. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermodegradable multisegmented polymer synthesized by consecutive radical addition‐coupling reaction of α,ω‐macrobiradicals and dithioester

A consecutive radical addition‐coupling reaction involving dithioester is applied to produce thermodegradable multisegmented polymer using α,ω‐dibromo polymer as precursor. The macroradical generated by single electron transfer process promoted by Cu/ligand from α,ω‐dibromo polymer can efficiently add to ethyl dithiobenzoate, which results intermediate adduct radical. The in situ formed adduct radical immediately undergoes crosscoupling reaction with macroradical, generating segmented polymer bridged with C? S bond. The consecutive radical addition‐coupling reaction generates multisegmented polymer linked by C? S bond following step‐growth mechanism. The multisegmented polymer can be thermodegraded in the presence of hydrogen atom donor or air. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Stereocontrolled Synthesis of (E)-β,γ-Unsaturated Esters via Palladium-Catalyzed Cross-Coupling of (E)-Alkenylboronic Acids with α-Bromoacetic Esters

The cross-coupling reaction of trans-alkenylboronic acids with a-bromoacetic esters was firstly studied. It was found that using Pd(OAc)2 as catalyst, a bulky electron-rich phospine, (2-dicyclohexylphospino-biphenyl) as ligand, the reaction can be readily accomplished to give specific (E)-b,g-unsaturated esters in high yields.     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Palladium‐catalyzed carbonylative cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with primary amines leading to N‐alkylmaleimides

Cyclic β‐bromo‐α,β‐unsaturated carboxylic acids are carbonylatively cyclized with primary amines under carbon monoxide pressure in MeCN in the presence of a catalytic amount of PdCl₂(PPh₃)₂ to give N‐alkylmaleimides. Copyright © 2012 John Wiley & Sons, Ltd.