SMALL RINGS .79. SYNTHESIS AND PROPERTIES OF NOVEL SILYL-SUBSTITUTED CYCLOBUTADIENES AND TETRAHEDRANES

The cyclobutadienes 2b, d as well as the corresponding tetrahedranes 3b, d have been prepared according to the ''Masamune route'' by starting from the diazo compounds 1b, d. Low-temperature C-13-NMR measurements of the cyclobutadienes 2a, b, d lead to the first exact values of the barrier heights in the interconversion of the two rectangular forms of the cyclobutadienes. Fluorodesilylation of 3d probably proceeds via tri-tert-butyltetrahedrane (3h) and cyclobutadiene 2h and finally yields diketone 18. Reaction of tetrahedrane 3d with LiAIH(4) in boiling THF leads to tetrahedrane 3e, which is much less stable than all previously known tetrahedrane derivatives.