Tetraalkyl cyclobutene-1,2,3,4-tetracarboxylates, prepared by intramolecular Wittig reaction between a vinylphosphonium salt and diethyl 2-oxobutanedioate, undergo electrocyclic ring-opening reactions, in boiling toluene, to produce highly electron-deficient 1,3-dienes.
Bicyclic alkenes, including Oxa- and azabicyclic alkenes can be readily activated by using transition-metal complexes with facial selectivity, because of the intrinsic angle strain on carbon-carbon double bonds of these unsymmetrical bicyclic systems. During last decades considerable progress has been done in the area of ring-opening of bicyclic strained ring by employing the concept of C-H activation. This Review comprehensively compiles the various C-H bond activation assisted reactions of oxa- and azabicyclic alkenes, viz., ring-opening reactions, hydroarylation as well as annulation reactions.
Stereoselective Synthesis of Tetraalkyl Cyclobutene-1,2,3,4-tetracarboxylates. Synthesis of Tetraalkyl (Z,Z)-Buta-1,3-diene-1,2,3,4-tetracarboxylates