ISOMERIZATION OF DIETHYL 1-ALKYNYLPHOSPHONATES TO 1,3-DIENYLPHOSPHONATES FOLLOWED BY DIELS-ALDER REACTION WITH DEAD, MALEIC ANHYDRIDE AND MALEIMIDE

摘要

Isomerization of diethyl 1-alkynylphosphonates, 1, with Pd[(PPh)3]4 in refluxing 1,4-dioxane provides 1,3-dienylphosphonates, 2, in satisfactory to excellent isolated yield (45-83%). The reaction is tolerant of chlorides and cyclic substituents. Cycloaddition reaction of 2 with DEAD provided the corresponding diethyl 3 -(diethoxyphosphoryl)-6-alkyl-3,6-dihydropyridazine-1,2-dicarboxylates, 3, in 85% isolated yield. The cycloaddition products can be obtained in a one-pot reaction directly from the isomerized 1-alkynylphosphonates with no loss in yields. Similarly, 1,3-dioxo-1,3,3a,4,7,7a-hexahydroisobenzofuran-4-ylphosphonate, and 1,3-dioxo-2,3,3a,4,7,7a- hexahydro-1H-isoindol-4-ylphosphonate 4 were obtained by reacting 1,3-dienylphosphonates with maleic anhydride and maleimide respectively.