Ring-expansion from tellurophenes to telluropyrans: inhibition of C–Te bond cleavages in transition metal-catalyzed reactions

Abstract

Tellurium-fused aromatic hydrocarbons have attracted numerous attention due to their unique properties as well as the synthetic challenges. However, the synthesis towards organotellurium molecules falls much behind those for other...

A Comprehensive Study on Redox Behavior and Halogen Exchange in Telluropyran Derivatives

“…After a Sonogashira coupling reaction [28] with ethynylbenzene and a following Stille coupling reaction, [29] the key intermediate 2‐(2‐(phenylethynyl)phenyl)‐tellurophene ( 2 ) was produced. Subsequently, via a ring‐expansion reaction catalyzed by Pt[P(C 6 F 5 ) 3 ] 2 Cl 2 , [27] the five‐membered tellurophene ring was expanded to a six‐membered telluropyran ring, and product T1 was afforded in yield of 82 %. It should be noted that telluropyran derivative T1 was quite stable in both solution and solid states.…”

“…N , N ‐dimethylformamide (DMF) was distilled from CaH 2 . Bis[tris(pentafluorophenyl)phosphine]platinum(II) dichloride [27] and 2‐(tributylstannyl)tellurophene [10] were synthesized according to previously reported methods. All reactions and manipulations were carried out with the use of standard inert atmosphere and Schlenk techniques.…”

“…In this work, a telluropyran derivative, i. e., 9phenylindeno[2,1-b]telluropyran (T1) (Scheme 1), has been synthesized via our previously developed ring-expansion reaction from corresponding tellurophene analogue. [27] The obtained telluropyran derivative is further oxidized into halogen adducts T1 * Cl 2 , T1 * Br 2 , and T1 * I 2 which can be chemically or thermally reduced to T1. The oxidation addition of telluropyran derivative T1 and the halogen exchange as well as the thermal elimination of the corresponding halogen adducts T1 * X 2 (X=Cl, Br, I) have been systematically investigated by UV-vis absorption titration, electrochemical measurements, thermogravimetric analysis, and density functional calculations.…”

“…In this work, a telluropyran derivative, i. e., 9‐phenylindeno[2,1‐ b ]telluropyran ( T1 ) (Scheme 1), has been synthesized via our previously developed ring‐expansion reaction from corresponding tellurophene analogue [27] . The obtained telluropyran derivative is further oxidized into halogen adducts T1•Cl 2 , T1•Br 2 , and T1•I 2 which can be chemically or thermally reduced to T1 .…”

Direct Access to Functionalized Azulenes and Pseudoazulenes via Unconventional Alkyne Cyclization Reactions

“…However, this cyclization reaction is deactivated by the electron deficient 4-trifluoromethyl phenyl group substituted on the alkyne. Later, the group successfully extended inserted heteroaromatic rings to include selenophene, [32] tellurophene, [33] and thieno[3,2-b]thiophene rings, [34] affording a series of novel pseudoazulenes containing these heavier chalcogen atoms (Scheme 16). It should be noted that due to the susceptibility of tellurophene to transition metal complexes, [35] PtCl 2 coordinated with strongly π-accepting phosphine ligand P(C 6 F 5 ) 3 was found to be the effective catalyst for ring expansion of tellurophenes to telluropyrans.…”