THE EFFECT OF PRESSURE ON THE CYCLOADDITIONS OF CYANOACETYLENE TO FURAN-DERIVATIVES - [2.2](2,5)FURANOPARACYCLOPHANE, [8](2,5)FURANOPHANE, AND FURAN

At 1 bar and 160 degrees C the reaction of cyanoacetylene (1) with [2. 2](2,5)furanoparacyclophane (3) produced the unexpected ''ring-enlarge d'' ketones 6-11. In the reaction of 1 with [8](2,5)furanophane (4) co mparable products 21 and 22 were observed, in addition to the products 19 and 20 expected from a consecutive Diels-Alder addition, Alder-Ric kert cleavage process and the Diels-Alder addition of 1,4-dicyano-1,3- cyclobutadiene (2a) to 4, respectively. In the reaction of 1 with the parent furan 5 only the (2:1) and (1:2) Diels-Alder adducts 23, 25, 26 , and 27 were found. High-pressure experiments and the reactivity of 2 -cyano-7-oxabicyclo-[2.2.1]hepta-2,5-diene (24), which was prepared in dependently by flow-thermolysis of the (1:2) Diels-Alder adducts 26 an d 27, provide evidence that the (2:1) adducts 20, 23, and 13 are proba bly formed by a sequence of Diels-Alder and [2 + 2] cycloadditions rat her than by the reverse sequence starting with [2 + 2] cyclodimerizati on of 1 followed by Diels-Alder reaction with cyclobutadiene 2a as pos tulated by the analogy to the trimerization of 1 and the cycloaddition of 1 to paracyclophane. The high-pressure experiments led us to propo se a new mechanism of formation of the ''ring-enlarged'' ketones 6-11.