Cross-coupling of a functionalized highly pyramidalized alkene: DSC and NMR study of the [2+2] retrocycloaddition of cyclobutane cross products, hyperstability and pyramidalization of the formed dienes

The synthesis, chemical trapping and ab initio calculations of the highly pyramidalized 5α,6α:11α,12α-bis(isopropylidenedioxy)pentacyclo[6.4.0.02,10.03,7.04,9]dodec-8-ene, 25, are reported. Its cross-coupling reaction with 3,7-dimethyltricyclo[3.3.0.03,7]oct-1(5)-ene, 1b, gave a cyclobutane derivative, 29, which on further manipulations gave the cyclobutane derivatives 32 and 33 and the derived [2+2] retrocycloaddition dienes, 31 and 34. Molecular Mechanics calculations show these dienes to be slightly pyramidalized but highly hyperstable. The neat conversion of 32 and 33 to 31 and 34, respectively, has been studied by DSC, 1H NMR and theoretical methods (MM2 and ab initio).