THIETANE AND SELENETANE COMPLEXES BY THERMAL CYCLOADDITION OF VINYL ETHERS TO TRANSITION-METAL-COORDINATED THIOALDEHYDE AND SELENOALDEHYDE - CRYSTAL-STRUCTURE OF NYL-2-OXA-8-THIABICYCLO[4.2.0]OCTANE-S)TUNGSTEN(0)

Pentacarbonyl(thiobenzaldehyde)tungsten und pentacarbonyl(selenobenzal dehyde)tungsten (1a and 1b) undergo a thermal [2+2] cycloaddition with several vinyl ethers to give highly substituted transition metal-coor dinated thietanes and selenetanes. The addition is highly regio- and s tereospecific. The products undergo acid-catalyzed rearrangements, whi ch lead to thermodynamically more stable diastereomers of the thietane s and selenetanes. The stereochemistry of both addition and rearrangem ent was established by reaction of deuterium-labeled vinyl ethers and by reaction of the cis and trans isomers of ethyl propenyl ether. The crystal structure of the bicyclic addition product of 1a and 3,4-dihyd ro-2H-pyran is reported.