Latent Nucleophilic Carbenes

Abstract

Using DFT and ab initio calculations, we demonstrate that noncyclic formamidines can undergo thermal rearrangement into their isomeric aminocarbenes under rather mild conditions. We synthesized the silylformamidine, for which the lowest activation energy in this process was predicted. Experimental studies proved it to serve as a very reactive nucleophilic carbene. The reactions with acetylenes, benzenes, and trifluoromethane proceeded via insertion into sp, sp2, and sp3 CH bonds. The carbene also reacted with the functional groups, such as CHO, COR, and CN at double or triple bonds, displaying high mobility of the trimethylsilyl group. The obtained silylformamidine can be considered as a latent nucleophilic carbene. It can be prepared in bulk quantities, stored, and used when the need arises. Calculation results predict similar behavior for some other silylated formamidines and related compounds.

Latent Carbene: Diaminomethylation of Thiophenes

“…Chemical behavior of thiophene resembles one of benzene. We have shown that 1,3‐dihalobenzenes reacted with silylformamidine 1 at the second position via nucleophilic insertion into C sp2 −H bonds [7] . Thus, we expected that an analogous reaction would occur with halosubstituted thiophenes.…”

“…We have shown that 1,3-dihalobenzenes reacted with silylformamidine 1 at the second position via nucleophilic insertion into C sp2 À H bonds. [7] Thus, we expected that an analogous reaction would occur with halosubstituted thiophenes. Indeed, we have found that trisubstituted halothiophenes 2 a, b readily reacted with silylformamidine 1 at room temperature for 2 days affording the corresponding aminals 3 a, b. Thiophene 2 a reacted with silylformamidine 1 at rt, the reaction come to completion in two days without any solvent or catalyst.…”

“…[12,13] In our previous work, we investigated the reaction of silylformamidine 1 with 1,3-dihalobenzenes. [7] It was shown that 1,3-disubstituted benzenes reacted always at the second position. Thus, we expected that thiophenes 14 would react analogously.…”

“…Halobenzenes were shown to actively react with silylformamidine affording aminals, and after hydrolysis the corresponding aldehydes. On the general, the more halogen atoms are present at benzene ring, the higher reactivity is observed [7] …”

“…On the general, the more halogen atoms are present at benzene ring, the higher reactivity is observed. [7] Silylformamidine 1 is a readily available reagent, as it can be prepared in bulk quantities and stored for a long time. Thus, we decided to further explore its application as a reagent for organic chemistry.…”