Synthesis of 1,1-Bis(3,5-Dimethyl-2-Furyl)Ethene - the Chemo-Selectivity and Site-Selectivity of Its Cycloadditions

The new polyene 1,1-bis(3,5-dimethyl-2-furyl)ethene (11) was derived from 2,4-dimethylfuran. Its reaction with dienophiles such as maleic anhydride, benzoquinone or 1-cyanovinyl acetate generated exclusively Diels-Alder adducts (9-oxabicyclo[4.3.0]nona-1,7-diene derivatives) involving the exocyclic double bond and one double bond of one furyl unit. The reaction of 11 with didehydrobenzene (benzyne) gave a 7-oxabicyclo[2.2.1]hepta-2,5-diene derivative resulting from the exclusive Diels-Alder addition of one furyl group, whereas dimethyl acetylenedicarboxylate added to 11 giving a mixture of the corresponding 7-oxabicyclo[2.2.1]hepta-2,5-diene and 9-oxabicyclo[4.3.0]nona-1,4,7-triene derivatives. With allenic acid, 11 added in a [2+2] fashion exclusively with its exocyclic double bond giving 2-[3,3-bis(3,5-dimethyl-2-furyl)cyclobutylidene]acetic acid with high selectivity.