Organophosphorus compounds, 138 - 3,5-dimesityl-1,2,4-oxadiphosphole - Synthesis and reactivity of a novel heterocycle

The first synthesis of a 1,2,4-oxadiphosphole 6 has been achieved by vacuum thermolysis of mesitylphosphaalkene 5. The novel heterocycle 6 exhibits an enormous potential for cycloaddition reactions, which predominantly procee d selectively at low temperatures. Compound 6 undergoes addition with two e quivalents of phosphaalkynes 10 by a [4+2] cycloaddition/homo Diels-Alder r eaction sequence to form novel oxatetraphosphadeltacyclenes 12 and 13. Tetr achloro-o-benzoquinone (14) undergoes a selective [4+1] cycloaddition with 12 and 13 leading to the spirocyclic products 15 and 16 containing lambda(5 )-phosphorus atoms. Treatment of the oxadiphosphole 6 with dimethyl acetyle nedicarboxylate (17) provides the first access to a 1,2-oxaphosphole 18, wh ich is formed after an initial [4+2] cycloaddition followed by a retro Diel s-Alder reaction. An unexpected reaction of 6 is observed with tri-tert-but ylazete (20) furnishing a new polycyclic system (--> 21).