[(1,3‐Dioxolan‐2‐yliden)methyl]phosphonate und ‐phosphinate als (einfache) Synthone in der Heterocyclensynthese

[(1,3‐Dioxolan‐2‐ylidene)methyl]phosphonates and ‐phosphinates as [ simple ] Synthons in Heterocyclic Synthesis The readily available [(1,3‐dioxolane‐2‐ylidene)methyl]phosphonates and ‐phosphinates 2a–f ( Scheme 1 ) can be transformed with amines to aliphatic ketene N,O‐and N,N‐acetales (see Scheme 2 , 2a → 3–7 ). Alkanediamines yield with 2a–f the imidazolidines 8a–f and the hexahydropyrimidines 9a–d ( Scheme 3 ). the oxazolidine derivatives 10a–e and the thiazolidine 11 are accessible under special reaction conditions starting from 2a, b ( Scheme 4 ). Hydrazines react with the CN‐group‐containing ketene O,O‐acetals 2a–c to the pyrazoles 12a–g , whereof 12a, d, e can be cyclized to pyrazolo[1,5‐ a ]pyrimidines 13a–d ( Scheme 5 ). Amidines as starting materials transform 2a–c in an analogous way to the pyrimidine derivatives 14a–c ( Scheme 6 ).