New reactions of carbon suboxide with alkynes

Abstract

Synthesis of 3,4,7,8-tetraalkyl-2-oxa-bicyclo[4.2.0]octa-1(6),3,7-trien-5-ones (4a-d), 4,5,7,8-tetraalkyl-2-oxa-bicyclo[4.2.0]octa-1(6),4,7-trien-3-ones (6a-d) and 3,4,7,8-tetraalkyl-2H,5H-cyclobuta[b]pyrano-[2,3-d]pyran-2,5-diones (7a-d) from the reaction of alkynes (1a-d) with carbon suboxide (2) in various molar ratios is described.J. Heterocyclic Chem., 40, 321 (2003).The reactions of carbon suboxide with different substrates have been extensively studied [1][2][3]. Recently our studies were concentrated on the reactions between carbon suboxide and some alkyne derivatives bearing either a hydroxy or an amino group, to synthesize heterocyclic compounds of potential biological interest [4].In this present paper we wish to report on the synthesis of some new bicyclo and tricyclo derivatives obtained by reacting carbon suboxide and alkynes in three different molar ratios.3,4,7,8-Tetraalkyl-2-oxa-bicyclo[4.2.0]octa-1(6),3,7-trien-5-ones (4a-d) and 4,5,7,8-tetraalkyl-2-oxa-bicyclo-[4.2.0]octa-1(6),4,7-trien-3-ones (6a-d) were obtained by reacting 0.032 mole of alkyne derivatives (1a-d) with 0.016 mole of carbon suboxide (2) in anhydrous chloroform solution. By using this ratio (2:1), yields are about 50%.The proposed reaction mechanism starts from the attack of 1a-d by 2 leading to the 4-oxomethylidene-2-cyclobuten-1-one derivatives (3a-d) followed by the attack of another 1a-d molecule to achieve the compounds (4a-d) and (6a-d). Although intermediates 3a-d were not isolated in this reaction, they have been previously reported by an Austrian researching group [5].Analogously, though in a previous paper we described the structure and stability of similar spiroalkandiones [6], any attempt to isolate 5a-d failed, since they rearranged to form 6a-d (Scheme 1).By reacting compounds 1a-d with 2 in a 1:2 molar ratio, we obtained a gummy product, that was probably a polymer or a macrocycle, along with a small quantity of 4a-d [7]. However, by reacting 1a-d with 2 in a 2:2.5 molar ratio, we obtained the new 3,4,7,8-tetraalkyl-2H,5H-cyclobuta[b]pyrano [2,3-d]pyran-2,5-diones (7a-d), and a