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6. - Iranian Journal of Organic Chemistry 2(2009 92-98 A...

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Iranian Journal of Organic Chemistry 2 (2009) 92-98 92 A facile synthesis of diastereoisomeric stable 1,4-diionic and also phosphorus ylides compounds contaning sulfur through the reaction between 1,3-dicarbonyl compounds with activated acetylenic esters in the presence of triphenylphosphine Malek Taher Maghsoodlou, Reza Heydari, Sayyed Mostafa Habibi Khorassani, * Mahmoud Nassiri, Jaber Salehzadeh, Sakineh Mollaee Poor and Mohammad Amin Kazemian Department of Chemistry, the University of Sistan and Balouchestan, P. O. Box 98135-674, Zahedan, Iran Abstract: The addition of triphenylphosphine to dialkyl acetylenedicarboxylates in the presence of 1,3-diethyl-2-thiobarbituric acid, cyclohexanone-2-carboxylate or 2-acetylcyclopentanone led to highly functionalized 1,4-diionic organophosphorus compounds and also stable phosphorus ylides respectively. These thio betaines possess two vicinal stereogenic centers and exist as a mixture of two diastereoisomers. The stable phosphorus ylides also exist in solution as a mixture of two geometrical isomers as a result of restricted rotation around the carbon-carbon partial double bond resulting from conjugation of the ylide moiety with the adjacent carbonyl group. Keywords: Ttriphenylphosphine, Acetylenic ester; 1,3-Dicarbonyl compounds; 1,4-Diionic phosphorus compounds; Stable phosphorus ylides; Diastereoisomer. Introduction In recent years there has been increasing interest in the synthesis of organophosphorus compounds, i.e. those bearing a carbon atom bound directly to a phosphorus atom [1-18] and [30-35]. This interest has resulted from the recognition of the value of such compounds in a wide range of industrial, biological and chemical synthetic aspects [28, 29]. As a result, a large number of methods have appeared novel synthesis of organophosphorus which involve 1,4-diionic phosphorus compounds as elusive transient species [5,19]. In all of the reactions in which this diionic system is postulated, the betaine cannot be isolated but appears to occur as an intermediate on the pathway to an observed product. We have previously described [20- 22] the synthesis of stable 1,4-diionic phosphorus compounds 1 from the reaction between triphenylphosphine and ethyl propiolate in the presence of CH-acids. With the purpose of preparation of betaines having two vicinal stereogenic center, such as 2 (see Scheme 1, previous work), The reaction between triphenyl- phosphine 3 and dialkyl acetylenedicarboxylates 4 with 1,3-diethyl-2- thiobarbituri acid 5 was undertaken for generation of 1,4-diionic 7 while stable phosphorus ylides 9 were obtained from reactions between 3 , 4 and 8 in excellent yields (See scheme 1). The thiobarbituric acid moiety and its derivatives have the important pharmaceutical property and they have been used for medicinal chemistry purposes [23].
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