The tetracoordinated hypervalent species named as σ- $sulfurane^1$ are relatively unstable and hence tend to transform, by extruding a ligand or two with a pair of electron, to stable compounds in which the central atom resumes a normal valency. It is best explained by a new ligand-coupling $concept^2$.
Since the ligand-coupling is clean-out reaction, it is also promising for the reduction of sulfilimines to the sulfides.
In order to elucidate the intermediate sulfurane derived from the reaction of N-(p-tolylsulfonyl) sulfilimines with lithium aluminum hydride, the reductions of various N-(p-tolylsulfonyl) sulfilimines with lithium aluminum hydride were carried out.
In order to see the relative reduction rate of S-(p-substitutedphenyl)-S-methyl-N-(p-tolylsulfonyl) sulfilimine, competitative reaction between various S-(p-substitutedphenyl)-S-methyl-N-(p-tolylsulfonyl) and S-methyl-S-phenyl-N-(p-tolylsulfonyl)sulfilimine with lithium aluminum hydride was carried out. The obtained ρ-value was +1.5.
The reaction appears apparently to be initiated via nucleophilic attack of the hydride on the trivalent sulfur. The initial back attack by hydride anion may form the σ-sulfurane contaning axial hydride ligand and then interconversion of the ligand takes place by pseudorotation to form the preferred sulfurane in which the hydride is replaced at an equatorial position and the $apicophilic^3$ benzyl group becomes an axial ligand in the incipient σ-sulfurane.
술필이민들과 리튬 알루미늄 수소 음이온과의 반응은 시그마-술푸란 중간체를 통한 리간드 결합에 의한 반응일것으로 추측된다. 시그마-술푸란 중간체들은 비교적 불안정 하기때문에 두개의 리간드가 유리된다음 술파이드들이나 사이올들같은 안정한 물질들로 변환 되어진다. 술핀이민의 환원반응에서 양의 로우 ( ρ ) 값은 수소 음이온의 술피닐 설퍼 공격이 율속단계 임을 암시한다.
근래에 알려진 많은 술푸란 중간체를 통한 리간드 결합 반응과 더불어 이 반응의 메카니즘 역시 매우 흥미로우며 술필이민의 환원에 유용한 반응이 될것으로 생각된다.
