β-Oxophosphoranes / ylides, versatile intermediates in synthetic organic chemistry can be prepared by the novel reaction of P-aryl cyclic phosphine oxides, such as 2,3-dihydro- and 2,3,4,5-tetrahydro-1H-phosphole 1- oxides, as well as 1,2-dihydrophosphinine 1-oxides with dialkyl acetylenedicarboxylates (DAAD). The reaction involves a spirocyclic oxaphosphete intermediate formed by the (2+2) cycloaddition of the P=O bond and the acetylene moiety and follows an inverse Wittig protocol that was evaluated by PM3 and Hartree-Fock ab initio quantum chemical calculations. The interaction of iminophosphine derivatives of the Martin ligand with acetylenic diacid esters follows a similar reaction path affording β-iminophosphoranes / ylides. In these cases, the azaphosphete is an intermediate, or one component of an equilibrium system. Another synthetic method for β- oxophosphoranes / ylides comprises the acylation of stabilised phosphonium ylides in position α. Under flash vacuum pyrolytic conditions, the b-oxophosphoranes / ylides are fragmented to the mixture of the corresponding acetylene and phosphine oxide. This reaction path is exactly the opposite of the formation of b-oxophosphoranes from a phosphine oxide and acetylene derivative that was mentioned above. Some other reactions of heterocyclic b- oxophosphoranes / ylides, such as reduction, deacylation and alkoholysis are also discussed that lead to valuable families of compound.