system (2, 4 and 7) apart from other unexpected products (3 and 5). In the case of the phosphole sulfide (1), the oxyallyl cation is believed to react preferentially with the P=S group, rather than the dienic moiety, leading to a P=S to P=O transformation or to a very particular reaction resulting in 5. This occurs through an intermediate (j) in which a C=S group reacts in a [2 + 4] cycloaddition with the