SYNTHESIS OF AZULENE-EQUIVALENT HETEROCYCLES BY [4pi+6pi] CYCLOADDITIONS

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1. Efficient synthetic procedures of 2-tert-butyl-6-(dimethylamino and acetoxy)fulvene was established, and reaction products between these compounds and several mesoionic compounds were scrutinized by the use of preparative liquid chromatography, which was purchased by the present grant.2. These reactions, as expected, gave condensed heterocycles which are isoelectronic with azulene, by [4pi+6pi] cycloaddition-extrusion-elimination reactions. A corresponding 2-unsubstituted fulvene also underwent this type of reaction though in lower yields.3. The reactions between 2-tert-butyl-6,6-dimethylfulvene and mesoionic compounds gave both [4pi+6pi] and [4pi+2pi] cycloadducts.4. In some reactions of the dimethyl derivative, interesting rearrangement products were formed in some cases. Structures of these products were firmly established by X-ray analyzes and other spectroscopic methods, and the mechanisms for their formation was discussed.5. A mesoionic 4-oxazolone gave an interesting oxygenated dimer on contact with a trace amount of oxygen. Its structure was determined by X-ray analysis.6. Spectral analyzes of these pseudo-azulene heterocycles showed that the electron distribution of these molecules are similar to that of azulene and the molecules are strongly polarized.7. These reactions have been analyzed on the basis of MNDO calculation results, and it was concluded that these reactions can proceed concertedly by both [4pi+6pi] and [4pi+2pi] fashion. This conclusion supports the view that a bulky substituent on the 2-position of fulvene ring strongly controls the periselectivity of these reactions.