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Novel annulation reactions for the synthesis of substituted pyrroles darzens reaction of acyl phosphonates with α-bromo ketones : selective synthesis of cis- and transepoxyphosphonates

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2009
Emrullah, Mustafa
In the first part of this thesis, it is aimed to develope methods for the synthesis of trisubstituted pyrrrole derivatives. 2-Aminopyrrroles, alkoxy and sulfonyl substittitued pyrrole derivatives as well as pirolinones show interesting biological activities and are precursor of well know drugs. Although there is a number of methods for the synthesis of pyrroles, the synthesis of 2-aminopyrroles is limited to few works and is not widely known. Therefore, it is still an important goal in organic chemistry to improve methods for the synthesis of multifunctionalized pyrrole derivatives and pyrrolinones. Alkylation of β-dicarbonyl compounds with bromoacetonitrile furnishes α- cyanomethyl-β-dicarbonyl compounds. The condensation reaction of α- v cyanomethyl-β-dicarbonyl compounds with amines catalyzed by p-TsOH affords the corresponding enamines and further base catalyzed cyclization furnishes 2- aminopyrroles in high yields, moreover, zinc perchlorate-catalyzed addition of amines, alcohols and thiols to the nitrile carbon of α-cyanomethyl-β-ketoesters followed by annulation gives the 5-alkoxy and 5-alkylsulfanylpyrrole-3-carboxylates in high yields. In the second part of the thesis, reactions of a broad range of acyl phosphonates with α-bromo acetophenones at room temperature in the presence of different bases were described to afford two diastereomeric epoxy phosphonates in good yields and high diastereoselectivities. The diastereoselectivity of this reaction is easily controlled by changing the base. Accordingly, changing the base from Cs2CO3 to DBU changes the diatereomeric ratio (trans/cis) from 5/3 to 9/1. Furthermore, the treatment of trans isomer with DBU shows a complete conversion to the corresponding cis isomer. Additionally, these highly functionalized epoxyphosphonates are shown to be useful intermediates to give several reactions