Formation of stable cyclic carboxonium salts in acylation of cyclopropanes

Abstract

It was found that the reaction of l,l,2,2-tetramethylcyclopropane (I) with pivaloyl tetrafluoborate (II) in CH2CI= at--50~ gives the stable carboxonium complex (!II) in 70% yield, mp 200-202 ~ (decompn.) (precipitated from CH=CI2 solution with dry ether). The structure of (III) was proved, by the data of the IH and 13C NMR spectra (the ~3C NMR spectra were obtained on a Varian CFT-20 instrument under the conditions of complete and partial noise decoupling from the protons). ~H NMR spectrum (6, ppm): 1.00s (6H~ CH3 at C~), 1.28 [9H, C(CH3)3], 155 s (6H, CH3 at C5), 3.71 s (2H, CH2). ~3C NMR spectrum (~, ppm): 245.5 s (C2), 123.2 s (C5), 53.9 t (CS), 42.3 s[C atom in C(CH3)a], 42.0 s (C4). 24.2 q (CHs in C(CH3)~), 20.9 ,q (CH3 at C5), 20.5 q (CH3 at C4).