A highly efficient method for solvent‐free synthesis of bisarylmethylidenes of pyranones and thiopyranones

Lewis Acids as Mild and Effective Catalysts for the Synthesis of 3,5‐Bis[(hetero)arylidene]piperidin‐4‐ones

“…Moreover, we failed to obtain 3,5-bis(4-fluorobenzylidene)piperidin-4-one (3a) in a reasonable yield using Et 2 NH instead of Me 3 SiNEt 2 in LiClO 4 -mediated synthesis ( Table 2, Entry 3). These data are in contrast to the reported procedure which led to more than 90% yield in the case of other aromatic aldehydes [8]. Better yields of 3a were obtained using BF 3 · Et 2 O either in combination with K 2 CO 3 in MeCN solution or in excess (6 equiv.…”

“…Therefore, if the starting substrates bear acid-or base-labile substituents such as CN, P(O)(OR) 2 , COOR, some heterocyclic moieties (e.g., furanyl) etc., the use of the above conditions would be unsuitable. Thus, several improvements have been achieved in the synthesis of bis(heteroarylidene)cycloalkanones by application of KF-supported reagents under microwave or ultrasonic irradiation [3], Pd/C-mediated synthesis [4], and Lewis acid catalysis including Me 3 SiI (TMSI) [5], Yb(OTf) 3 [6], LiClO 4 in the presence of amines [7], and MgBr 2 · Et 2 O/ MeOH/Et 3 N [8], as well as SmI 3 [9] and FeCl 3 [10] in ionic liquids. Strangely enough, the data concerning improvements of the synthesis of 3,5-bis[(hetero)arylidene]piper-idin-4-ones, which would be more advantageous for further modifications, are restricted to only one report on LiClO 4 -mediated condensation of NH-piperidin-4-one with aromatic aldehydes and thiophene-2-carbaldehyde in the presence of Et 2 NH and under solvent-free conditions [7].…”

A highly efficient method for solvent‐free synthesis of bis(arylmethylidene)piperidinones

“…Formation of the enolate in this mechanism is supported by the fact that both the Lewis acid and the amine are required for the reaction to proceed and in the absence of any of them no product is obtained. Such mechanism can also be concluded from similar aldol condensations previously conducted under Lewis acid/amine catalysis [14][15].…”

“…Despite the importance of these compounds from biological and bioorganic points of view [9][10], they have been prepared via the condensation of 1c-e with aromatic aldehydes under relatively harsh conditions and after long reaction time periods [9][10][11]. Our interest to develop the chemistry of heterocyclic systems [12] recently led us to report convenient procedures for the preparation of bisarylmethylidenes of thiopyranone 1c and pyranone 1d systems under lithium perchlorate (LiClO 4 ) [13] or magnesium bromide ethyl etherate [14] mediation. In continuation of these studies, we would like to report now a mild and general procedure for rapid synthesis of bisarylmethylidenepipyridinones at room temperature.…”

Biginelli reaction for synthesis of novel trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes

“…Particularly, some of the fluorine-containing heterocycles have been known with potential interesting medicinal and agricultural applications [34][35][36]. In the frame work of our program to develop the chemistry of heterocyclic compounds [37][38][39][40][41][42] and in connection with our ongoing interests in MCRs [43][44][45][46][47][48], we would like to introduce a facile procedure for the synthesis of trifluoromethyl derivatives of bis(tetrahydropyrimidinone)benzenes via one-pot condensation of terephthalic aldehyde with (thio)urea or guanidine and fluorinated 1,3-dicarbonyl derivatives (Scheme 1). The reaction proceeds at ambient temperature using catalytic amount of TMSCl to afford high yields of the title compounds in short time periods.…”