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C 0 M M U N I C AT1 0 N S pectation that even a cyclopropenyl radical with 3x-electrons has antiaromatic characterf5! By known methods[61 we have prepared di-tert-butyl-(3,5-ditert-butylpheny1)cyclopropenylium perchlorate ( 1 1 and from this by means of LiAIH4 1,3-di-tert-butyl-2-(3,5-di-tert-butyl-pheny1)cycloprepene (2). Photolysis of a solution of (2) in di-tert-butyl peroxide['] at -30°C affords a radical (3) whose Dedicated to Professor K. Dimroth on the occasion of his 65th birthday The simplest representatives of previously known antiaromatic[*} compounds are the 4x-electron systems cyclobutadiene and the cyclopropenyl anions bearing substituents that force the carbanion center to adopt a planar configuration. Calculations by the electron gas method[31 and MO calculations with consideration of overlap integralsc4] lead to the ex-Fig. 1. ESR spectrum of the di-tert-butyl-(3,5-d1-tert-butl.lphenyl)cyclopropenyl radical (3) in di-tert-butyl peroxide at -30°C.

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a) After 6 h the resulting (3) is filtered off [yield ca. 38 %, m. p. 140°C (dec.)] and compound ( 4 ) vacuum-distilled [yield 49%, b.p. 113°C/10-3 torr]. b) After 6 h isopropanol (10ml) is added and the mixture stirred for 3 h before evaporating to dryness. The residue is taken up twice in n-pentane (2 x 50ml), filtered hot, and the filtrate cooled to -78 "C, whereupon compound ( 5 ) crystallizes [yield 37 %, m.p. 104"C].