Synthesis of some 1,3,5-cycloheptatriene derivatives from tropylium hexachlorophosphate chloride

Abstract

The cycloheptatriene fragment enters into various biologically active compounds, in particular, efficient antimitotic agents [ 1,2] used in the chemotherapy of malignant tu-In this connection, development of new methods for the synthesis of compounds belonging to the class ofcycloheptatrienes is of current interest.A key role in the synthesis of 1,3,5-eycloheptatriene derivatives belongs to tropylium salts (bromide, perchlorate, tetrafluoroborate) which are typically obtained by involved multistage processes. From the practical standpoint, the double salt of tropylium hexachlorophosphate chloride [4] is more available. As will be shown below, this substance can be successfully used for the synthesis of a number of substituted cycloheptauienes by the following scheme: ported earlier [5] for the interaction of malonodinitrile with tropylium bromide. The synthesized compounds appear for the most part as transparent mobile liquids with a sharply irritating odor. The proposed structures were confirmed by the results ofphysicochemical analyses. In particular, the IH NMR spectrum of compound IIa contains a singlet due to protons of the methoxy group at 8 = 6.36 ppm. Protons of the seven-membered cycle are manifested as four groups of signals with chemical shifts ~ = 6.36, 5.70, 5.13, and 2.97 ppm. The spectrum is generally similar to that reported for a compound obtained by the interaction oftropylium perchlorate with methanol [6].Interaction of compound IIa with phosphorus pentachloride leads to compound I in quantitative yield. The proposed structure was confirmed by conversion of the product into tropylium tetrafluoroborate using the method described in [7]: 494The physicochemical properties of the synthesized compounds II -VII are presented in Table I.In order to determine the effect of substituents in 1,3,5-cycloheptatriene on the proton chemical shifts, we have synthesized the unsubstituted 1,3,5-cycloheptatriene [8]. The IH NMR spectrum of this compound displays signals of four types" (I) A triplet due to protons in position 7 with 5 = 2.25 ppm (J7-6 = J7-I -~ 6 -7 Hz).(2) A multiplet due to protons in positions 1 and 6 with 5 = 5.35 ppm (J1 -z = J5-6 ~ 10 Hz; JT-1 = J7-6 = 6 -7 Hz).(3) A multiplet due to protons in positions 2 and 5 with 5 = 6.20 ppm. This multiplet allows us to readily determine the spin-spin coupling constants (JI -z = Js-6 ~ 10 Hz).