Allenylphosphonates useful precursors of pyrazoles and 1,2,3-triazoles

Abstract

The synthesis of new pyrazoles and triazoles, with or without phosphorus substituents, from allenylphosphonates is described. Thus, Ph3P-promoted reactions of the allenylphosphonates (OCH2CMe2CH 2O)P(O)CH=C=CRR′ [R = H, R′ = Me (1b), R = R′ = Me (1c)] with DIAD/DEAD lead to phosphonopyrazoles by utilizing the -CO 2R functionality of DIAD/DEAD for cyclization. The products derived from allenylphosphonates with an α-phenyl group undergo an unusual but facile P-C bond cleavage to form tetrasubstituted pyrazoles. In the second type of reaction, Me3SiN3 reacts with the allenylphosphonates to form phosphono-1,2,3-triazoles in CH3CN at reflux, whereas (β-azidoallyl)phosphonates were obtained in high yields at room temperature. These latter compounds undergo cycloaddition with activated acetylenes to afford multisubstituted 1,2,3-triazoles. They were subsequently transformed into diverse N-substituted 1,2,3-triazoles through the Horner-Wadsworth-Emmons reaction. The structures of the key compounds were established by X-ray crystallography. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.