STEREOCONTROLLED SYNTHESIS AND CYCLOADDITION OF 1,4-DIALKOXY 1,3-DIENES

An efficient and stereocontrolled access to 1(Z),3(E)-1,4-dialkoxybuta dienes is described that relies on a base-induced conjugated eliminati on reaction on y-alkoxy or aryloxy a,a-unsaturated acetals. The dienes have then been applied in [4 + 2] cycloaddition reactions where they demonstrate a good thermal reactivity toward activated dienophiles. De spite the 1,4-competition between oxygenated groups, both regio- and e ndoselectivities are total. A set of experiments has led to the conclu sion that the (1Z,3E) pattern is responsible for these high stereocont rols. Several chiral alkoxy dienes have also been prepared following t he same route. Their thermal cycloaddition with N-methylmaleimide lead s to corresponding adducts in good yields and with total endoselectivi ties, but modest diastereoisomeric excess.