No Acid Required: 4蟺 and 6蟺 Electrocyclization Reactions of Dienyl Diketones for the Synthesis of Cyclopentenones and 2H-Pyrans
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- 作者：Steven D. Jacob ; Joshua L. Brooks ; Alison J. Frontier
- 刊名：Journal of Organic Chemistry
- 出版年：2014
- 出版时间：November 7, 2014
- 年：2014
- 卷：79
- 期：21
- 页码：10296-10302
- 全文大小：421K
- ISSN：1520-6904
文摘
The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4蟺) or 6蟺 electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6蟺 cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4蟺 and -6蟺 electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations.