Efficient Synthesis of 2-Iodo and 2-Dicyanomethyl Derivatives of Thiophene, Selenophene, Tellurophene, and Thieno[3,2-b]thiophene

Abstract

An effective synthesis of 2-iodothiophene, 2-iodotellumphene, and 2iodothieno[3,2-blthiophene and a Pd-catalyzed carbon-carbon coupling reaction of these iodo derivatives as well as 2-iodosclenophene with malononitrile affording novel thienyl-, tcllurienyl-, thieno[3,2-blthienyl-, and selenienylmalononitrile are described.Thesc heteroarylmalononitn'les are important synthons for the preparation of Zdicyanomethylene-2,5dihydroheterophene chromophores.In recent years, heterocycle-incorporated conjugated molecules exhibiting interesting electrochemical and optical properties have been widely developed in the field of pure and applied chemistry.lm e Pd-or Nicatalyzed carbon-carbon bond formation,2 a key stage in the synthesis of many currently interesting heterocycle-incorporated compounds, has proved to proceed generally and effectively by using the iodo derivatives of the corresponding heteroaromatic compounds.However, the existing methodologies for the preparation of 2-iodothiophene (113 and 2-iodothieno[3,2-blthiophene (414 were limited ta the use of toxic mercuric oxide-iodine combination and 4 was obtained in only 20% yield.5 Iodination of tellurophene was performed with b.ans-1-chloro-2-dichlomiodoethylene, but it was problematic in giving 2-iodotellurophene(3) in a very poor yield of 7%.6We have now found more convenient and effective synthetic methods for 2-heteroaryl iodides (I), (3), and (4), without using toxic yellow mercuric oxide, which are important compounds for the preparation of heterocyclic derivatives via low-valent transition metal catalyzed carboncarbon cross-coupling reactions.Heteroarylmalononitriles, capable of acting as key synthetic precursors for a building block of heterocycle-extended electron acceptors,7 have never been reported to date, although