8-Phosphabicyclo[3.2.1]octanes-III⁴. The reaction between oxyallyl cations and phosphole derivatives

The reaction of oxyallyl cations with phosphole sulfide as well as phosphole oxides was investigated and was found to give the expected 8-phosphabicyclo[3.2.1]octanic 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 phosphole as a diene. The structure and stereochemistry of the various products were established by the aid of their spectral data in conjunction with spectral data of some related compounds. A formal PhPO elimination is believed to occur through an intermediate phosphinate resulting from Bayer-Villiger like oxidation, which then loses the [PhPO₂] group. Phosphole sulfide (1), previously found to react as a dienophile, was shown to enter a [2 + 4] cycloaddition as a diene with powerful dienophiles like 4-methyl-1,2,4-triazoline-3,5-dione (10).