Thermal oligomerization of methyl 4-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)buta-2,3-dienoate

Abstract

Dimeric compounds formed as a result of thermal oligomerization of methyl 4-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)buta-2,3-dienoate were identified.Cyclobutane derivatives attract increased attention of many researchers. This is related to both specific structure and chemical properties of compounds containing a cyclobutane ring and their possible application in medicine, primarily as antiviral and antitumor drugs [1,2]. Interest in such structures stimulates development of simple, inexpensive, and general procedures for their preparation with a view to obtain new derivatives, taking into account that the number of available cyclobutane compounds is not large. Substituted allenes were shown [3] to be promising as starting compounds for the synthesis of cyclobutane derivatives [3].In the present work we studied transformations of allene II having a phthalimide fragment, which was synthesized by the Wittig reaction of N-phthaloylglycine (I) prepared in turn by direct fusion of phthalic anhydride with glycine (Scheme 1). The Wittig reaction of I afforded 63% of allene II and 5% of ylide III. The structure of the products was proved by spectral data. The 1 H NMR spectrum of II contained doublet signals at δ 6.21 and 7.25 ppm due to protons in the allene fragment, and the allene carbon atoms gave signals at δ C 91.75, 96.66 (-CH=), and 209.97 ppm (=C=) in the 13 C NMR spectrum.It is known that thermal activation of allene leads to its dimerization [3,4]. Heating of allene II in boiling toluene under microwave irradiation and without it, as well as under polymerization conditions in the presence of azobis(isobutyronitrile) (AIBN) and in the absence of initiator, gave substituted cyclobutanes IV-VI (Scheme 2). Joint oligomerization of allenes with unsaturated compounds is known to produce methylenecyclobutane and methylenecyclobutene derivatives [3,4]. In our case, the reaction of allene II with dimethyl acetylenedicarboxylate resulted in dimerization of the allene rather than in co-oligomerization (see table). The structure of the dimeric products was determined by IR and NMR spectroscopy, mass spectrometry, and elemental analysis.The 1 H NMR spectra of IV and V contained two three-proton singlets from methyl protons in the two nonequivalent ester groups at δ 3.29, 3.79 and 3.37, 3.76 ppm, respectively, which indicated formation of