| Research Abstract |
1. Regioselectivity of nucleophilic addition to conjugated Allenic ketones, 4,5-heptadien-3-one, 2,6-dimethyl-4,5-heptadien-3-one, and 5-phenly- and 5,5-diphenyl-3,4-pentadien-2-one, depends strongly on the nucleophile: anionic nucleophiles, e.g., triethylamine salts of benzenethiols, gave the <beta>-substituted , -unsaturated ketones with high selectivity. In contrast, neutral nucleophile molecules, e.g., benzenethiols or aniline, affoded the <beta>-substituted <alpha>,<beta>- unsaturated ketones. The reactions to allencearbocylic rdyrt, methyl 2,3-pentadienoate and methly 4-methyl-2,3-pentadienoate, indicated the same regiochemical tendency, but lower selectivities were observed in the reaction with benzenethiol. The reactivities of allenic ketones,esters, and nitriles decreased in the order. The above regiochemical selectivities of the nucleophilic additions can reasonably be explained by assuming the dienolate anions and dienols as reaction intermediates.
2. A new method for preparing 3-substituted 2-pyrones has been realized by theDBU-catalyzed Michael addition of dimethyl malonate, methyl acetacetate, and methyl cyanoacetate to an allenic ketone, 4,5-heptadien-3-one. This result was also consistent with the proposed reaction mechanisms of the regiochemical selectivity.
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