Preparation and characterisation of alkylthio- and phenylthio-phosphetan 1-oxide derivatives. Mass spectrometric investigations of 40 phosphetan 1-oxide compounds. Differentiation of cis- and trans-ring methyl groups by aromatic shielding

Abstract

Nine new 1-alkylthio-2,2,3,4,4-pentamethylphosphetan 1-oxide derivatives, C₈H₁₆P(O)X, have been prepared and fully characterised by i.r. (resulting in some improved assignments), p.m.r., ³¹P n.m.r., and especially by mass spectrometry. This last technique has been extended to cover 40 phosphetan 1-oxide compounds of various types. The breakdown pattern is shown to be essentially the same in all cases being largely governed by the fragmentation of the hydrocarbon moiety. An important rearrangement ion is observed which arises from the migration of the group on phosphorus exocyclic to the ring, X, to the hydrocarbon chain. The extent of this rearrangement depends upon the P–X bond strength and the steric crowding associated with X. The compounds C₈H₁₆P(O)SPh and C₈H₁₆P(O)SCH₂Ph exhibit long-range n.m.r. deshielding and shielding of the phosphetan proton and methyl groups respectively by the ring currents of the aromatic component. In the benzylthio-compound this also serves to distinguish for the first time the cis- and trans-methyl groups.