No Acid Required: 4π and 6π Electrocyclization Reactions of Dienyl Diketones for the Synthesis of Cyclopentenones and 2H-Pyrans
نویسندگان
چکیده
The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π 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 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and -6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations.
منابع مشابه
Solvent-Free Multicomponent Reactions of Dithiocarbamates, Activated Acetylenes and Isocyanides
An efficient method to synthesis the 2H-pyrans using three component reactions of dithiocarbamats, activated acetylenes and isocyanides in water as the solvent is described. In these reactions, synthesis of 2H-pyrans is possible based on the one-pot reaction and without using any catalyst. The mild reaction conditions and high yields of the products exhibit synthetic advantage of these methods.
متن کاملCatalytic Asymmetric Piancatelli Rearrangement: Brønsted Acid Catalyzed 4π Electrocyclization for the Synthesis of Multisubstituted Cyclopentenones.
The first catalytic asymmetric Piancatelli reaction is reported. Catalyzed by a chiral Brønsted acid, the rearrangement of a wide range of furylcarbinols with a series of aniline derivatives provides valuable aminocyclopentenones in high yields as well as excellent enantioselectivities and diastereoselectivities. The high value of the aza-Piancatelli rearrangement was demonstrated by the synthe...
متن کاملApplication of Green Chemistry in Synthesis of Functionalized Thiopyran viaOne-pot Multicomponent Reactions in Water
An efficient synthesis of 2H-thiopyran-3,4-dicarboxylate derivatives via one-pot reactions between acetylenic esters, arylisothiocyanates and enaminones in water is described.The advantages of this work were: (1) the reaction was performed under neutral and more important in water as the solvent. (2) No catalyst was required for this reaction. (3) The simplicity of the present procedure made it...
متن کاملElectrocyclization of cis-dienals in organic synthesis: a new and versatile synthetic method for the preparation of aryl- and heteroaryl-fused coumarins.
Benzo-, furo-, thieno-, and pyrido[f]coumarins were prepared by generating the 2H-pyran-2-one moieties from the oxidation of the corresponding 2H-pyran rings, which were formed in situ from the electrocyclization of cis-dienals.
متن کاملA new method for synthesis of tetrahydrobenzo[b]pyrans and dihydropyrano[c]chromenes using p-dodecylbenzenesulfonic acid as catalyst in water
p-Dodecylbenzenesulfonic acid (DBSA) was used as a catalyst for a simple and efficient one-pot synthesis of aryl substititued tetrahydrobenzo[b]pyrans and dihydropyrano[c]chromens via initial Knoevenagel, subsequent Micheal and final heterocyclization reactions of aryl aldehyde, malononitrile and 4-hydroxycoumarin/dimedone in moderate to excellent yields. The present method was operationally si...
متن کامل