Heterodiene syntheses. Part 20. 4-Arylidene-5-pyrazolones and ynamines : a [2 + 2]cycloaddition followed by electrocyclic ring opening, in competition with a [4 + 2]cycloaddition; the influence of the substituents on the intermediate
- 1 January 1979
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- p. 856-862
- https://doi.org/10.1039/p19790000856
Abstract
4-Arylidene-5-pyrazolones (1) react with NN-diethylaminomethylacetylene to give a mixture of pyrano[2,3-c]pyrazoles (3), in accordance with a [4 + 2]cycloaddition, and 4-(3-aryl-1-diethylamino-2-methylpropenylidene)pyrazol-5-ones (5) which are formed by electrocyclic ring opening of the [2 + 2]cycloadducts (4). The configuration of the open-chain compounds (5) permits the deduction of that of the originally formed cyclobutene adducts. The reason for the choice between a [4 + 2] and a [2 + 2] cycloaddition can be rationalized in terms of the effect of both the substituents and the configuration of the substrate.Keywords
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