Synthesis and Properties of Selenoiminium Salts Derived from Secondary Selenoamides

A variety of N-monosubstituted selenoiminium salts were obtained by reacting the
corresponding secondary selenoamides with methyl triflate at room temperature for 30 s.
All of the salts were stable under air below room temperature. The structures of the
selenoiminium salts were determined by X-ray molecular analysis and compared with those
of the starting selenoamide and its anionic derivative, i.e., an ammonium selenoimidate.
Their benzene rings and selenoamide moieties were found to not be planar. 13C and 77Se
NMR spectra of these compounds were also compared, and the results suggested that the
electrons on the selenium atom of the salts are somewhat delocalized to the CN double
bond and the carbon−selenium bond of the salts shows a partial double-bond character.
The degree of the delocalization of the electrons can be explained by considering the electron-donating ability of the selenium atom and the electron-accepting ability of the carbon−nitrogen bond. The reaction of the selenoiminium salt with several bases gave the
corresponding methyl selenoimidate in high yield. Methylation of an ammonium selenoimidate also gave the methyl selenoimidate. The Z-isomer was predominantly formed in exactly
the same ratio in these different reactions. The stereochemical outcome of the formation of
a methyl thioimidate formed by two different reactions is also discussed.

将相应的仲硒代酰胺与三氟甲磺酸甲酯在室温下反应30秒，即可得到多种N-单取代硒代亚胺鎓盐。所有该类盐在室温以下的空气氛围中均稳定存在。通过X射线分子结构分析确定了硒代亚胺鎓盐的分子结构，并将其与起始原料仲硒代酰胺及其阴离子衍生物——硒代亚胺酸铵——进行了对比。研究发现，其苯环与硒代酰胺基团并不共平面。对这些化合物的¹³C与⁷⁷Se核磁共振波谱进行了对比分析，结果表明该类盐中硒原子上的电子可一定程度离域至C=N双键，且其碳-硒键表现出部分双键特性。电子离域程度可通过硒原子的给电子能力与碳-氮键的吸电子能力进行解释。该硒代亚胺鎓盐与多种碱反应，可高产率得到相应的硒代亚胺酸甲酯。对硒代亚胺酸铵进行甲基化反应，同样可得到硒代亚胺酸甲酯。在上述不同反应中，均主要生成Z型异构体，且其生成比例完全一致。此外，本文还讨论了通过两种不同反应制备硫代亚胺酸甲酯时的立体化学结果。