A General Synthesis of (Z)‐1,2‐Ethenediol Derivatives

By retro‐Diels‐Alder reaction of suitably substituted 9,10‐dihydro‐9,10‐ethanoanthracene‐cis‐11,12‐diol derivatives (4, 6, 8, 10, 12, 14) a number of known and unknown (Z)‐1,2‐disubstituted ethenes (5, 7, 9, 11, 13, 14) have been prepared in high yield, including derivatives with two different substituents. In contrast to this, attempts to prepare 1,3,2‐dioxasiloles bearing only substituents on the silicon atom gave dimers containing the ten‐membered ring system (Z,Z)2,2,7,7‐tetraalkyl‐1,3,6,8‐tetraoxa‐2,7‐disilacyclodeca‐4,9‐diene (19b, 21b, 23b, 25b). Again these compounds are formed diastereoselectively with respect to the double bonds.