Synthesis of Five-Membered Cyclic Phosphinic Acids via the [4C+1P] Cyclization of 1,3-Dienes with a Combination of PBr 3 and P(OMe) 3 as the P (III) Source.

An efficient method for the synthesis of 1-hydroxy-2,5-dihydrophosphole 1-oxides, a type of five-membered P -containing heterocyclic compound, is presented. The reaction was carried out through a [4C+1P] cyclization of 1,3-dienes with a combination of PBr 3 and P(OMe) 3 as the P (III) source. To compare with the reported methods, the protocol reported herein not only is much milder and more rapid but also displays a broad substrate scope and affords the products in high yields (50-94%). In addition, the reaction could be reliably scaled up at the gram-scale level and was demonstrated to be a versatile platform for flexible derivatization. Consequently, this method provides a general and reliable way for the synthesis of five-membered phosphole derivatives.