A PALLADIUM(0)-SAMARIUM(II) SYSTEM FOR THE PREPARATION OF ALLENES FROM PROPARGYLIC ACETATES - APPLICATION TO THE SYNTHESIS OF 2,3-NAPHTHOQUINODIMETHANES

The selective conversion of 1,2-bis(1'-acetoxy-2'-propynyl)benzene der ivatives to the corresponding 1,2-diallenylbenzenes with the aid of a palladium(0)-samarium(II) reduction system leads to a new route to fai rly reactive o-naphthoquinodimethanes derivatives under mild condition s. The reactions of these naphthoquinodimethanes were found to follow different paths depending on the nature of the substituents on the ter minal acetylenic carbon atoms. They undergo intermolecular Diels-Alder reactions with various dienophiles, intramolecular [2+2] cycloadditio ns, or intramolecular [1,5]-sigmatropic hydrogen shifts.