[4 + 2] Cycloaddition of Vinylphosphine Oxides to α-Oxy- o-xylylene as a route to Phosphorylated Naphthyl and Biaryl Scaffolds.

α-Oxy- o-xylylene, a highly reactive diene readily accessible from benzocyclobutenol, undergoes Diels-Alder reaction with vinylphosphine oxides, yielding the corresponding 2-phosphorylated 1-hydroxy-1,2,3,4-tetrahydronaphthalenes in excellent yields. Use of unsubstituted and trans-2-aryl-substituted vinylphosphine oxides leads to cycloadducts with complete regioselectivity and with cis/trans selectivity up to 19:1 in the most favorable case. In the case of P-stereogenic trans-2-aryl-substituted vinylphosphine oxides, a virtually complete chirality transfer from P to C can be achieved. Dehydration and aromatization of the obtained cycloadducts bearing the resolved P-stereogenic phosphinoyl groups can be carried out to afford the valuable P-stereogenic and axially chiral phosphorylated 1,2'-binaphthyl ring system. Cases of restricted rotation around Csp3-Csp2 single bond in some tetrahydronaphthalene cycloadducts have also been revealed.