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■ Isomerization of Diethyl 1-Alkynylphosphonates to 1,3-Dienylphosphonates Followed by Diels-Alder Reaction with Dead, Maleic Anhydride and Maleimide

Abdullatif Azab, Abed Al Aziz Quntar, Tamar Antebi, and Morris Srebnik*

*Institute of Drug Research, School of Pharmacy, The Hebrew University of Jerusalem, P. O. Box 12065, Jerusalem 91120, Israel

Abstract

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.