ofsolvent, and chromatography of the residue with light petroleum on S O z gives (3) (135mg, 22 %) as yellow crystals. Received: March 2, 1978 [Z 984a IE] German version: Angew. Chem. 90, 551 (1978) CAS Registry numbers: ( I ) , 36319-94-5; (2), 66808-99-9; ( 3 ) , 66809-00-5; (41, 66809-01-6; ( 5 ) , 66809-02-7 [ I ] Small Rings, Part 24. This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. We are indebted to Ms. U . Stanior for experimental assistance.-Part 23: G. [4] U . Schollkopfin Houben/Weyl: Methoden der organischen Chemie, Vol. XIII/l. Thieme, Stuttgart 1970, pp. 3-25, 87-253; M. Schlosser: Struktur und Reaktivitat polarer Organometalle. Springer, Berlin 1973. [5] An analogous phenyl shift is considered as a possibility in the reaction of tetracyclone with phenyllithium: A. K . Youssef, M. A. Ogliaruso, J. Org. Chem. 37, 2601 (1972).

5 ) : 66809-02-7.( 1 ) : 36319-94-5 J (2): 66808-99-9 J ( 3 ) : 66809-00-5 J ( 4 ) : 66809-01-6 J [I] Kleine Ringe, 24. Mitteilung. Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft und vom Fonds der Chemischen Industrie unterstutzt. Frau U . Sranior danken wir fiir experimentelle Hilfe. -23.

Es wird uber die erste Synthese eines durch sterisch anspruchsvolle Substituenten stabilisierten Tetrahedrans berichtet. Das Tetra-terr-butyl-Derivat 37 entsteht bei der Belichtung von Tetra-ferrbutylcyclopentadienon (26), welches seinerseits aus dem bereits bekannten Cyclopentadienon 5 aufgebaut werden kann. Das Tetrahedran 37 bildet farblose bestandige Kristalle und geht bei 135 "C in das entsprechende Cyclobutadien 36 uber. Diese Valenzisomerisierung ist photochemisch umkehrbar. Small Rings, 38 1 ) Tetra-tert-bu tyltetrahedraneThe first synthesis of a tetrahedrane stabilized by sterically demanding substituents is described. Tetrahedrane 37 originates from irradiation of tetra-fert-butylcyclopentadienone (26), which can be prepared starting from the already known cyclopentadienone 5 . It forms colourless stable crystals. At 135 "C tetrahedrane 37 valenceisomerizes to the corresponding cyclobutadiene 36. This reaction can be reversed photochemically.

Die Konstitution der Titelverbindung 1 wird zweifelsfrei aus den spektroskopischen Daten abgeleitet. Small Rings, 391)

The stable tetrahedrane derivative (3)—the very first alkyl‐substituted tetrahedrane—has now been synthesized photochemically from the cyclopentadienone (1). 1H‐NMR, 13C‐NMR, mass, and IR spectra, as well as the reversible isomerization to (2), are compatible with the tetrahedrane structure. The unexpected stability of the compound is attributed to substitution of all four corners of the skeleton with bulky groups.—The starting material (1), which is also new could only be prepared under “forbidden conditions”.