Condensation reactions arylaldehydes

As mentioned in Section 11.20.5.1 discussing the reactivity of these ring systems, the ring closure reactions to 53-55 have been coupled in several cases with subsequent condensation reactions with arylaldehydes to yield benzylidene derivatives of these ring systems (e.g., 13) which transformations can be considered as cascade reactions. 

Claisen condensation org chem 1. Condensation, in the presence of sodium ethox-ide, of esters or of esters and ketones to form p-dicarbonyl compounds. 2. Condensation of arylaldehydes and acylphenones with esters or ketones In the presence of sodium ethoxide to yield unsaturated esters. Also known as Claisen reaction. klas-3n kand-on sa-shon ... 

Formation of 1,2,4-oxadiazines occurs by acid-catalyzed ring expansion of a-aziridino oximes and dioximes, and by 1,3-dipolar cycloaddition of arylcarbonitrile oxides and 2-acyl-2//-azirines (Section 6.14.10). Preparation of l,2,4-oxadiazin-5-ones can be achieved by ring closure of A-carboxymethyl and A-alkoxycarbonylmethyl amidoximes (Section 6.14.9.1.1), by the acid-catalyzed condensation of arylaldehydes with O-alkyl-A-acylhydroxylamines (Section 6.14.9.2.3.1), and by reaction of A-hydroxyureas or amidoximes with a two-carbon fragment such as an a-halo ester or an acyl halide (Section 6.14.9.2.2.1). 

MSA can be used as a powerful, safe, and recyclable catalyst for the condensation reaction of cyclic 1,3-diketones with arylaldehydes (Scheme 3.25). Firstly, synthesis of 2,2-(arylmethylene)bis(3-hydroxycyclohex-2-enone) from reaction of cyclic 1,3-diketones with several aromatic aldehydes was expected, but, as can be seen from Scheme 3.25, under the given conditions, 2,2 -(arylmethylene)bis(3-hydroxycyclohex-2-enone) was not formed and cyclic 1,3-diketones with aldehydes were effectively cyclized to give 9-aryl-substituted 1,8-dioxooctahydroxanthenes. 

Fringuelli, R, Pani, G., Piermatti, 0. and Pizzo, R, Condensation reactions in water of active methylene compounds with arylaldehydes, Tetrahedron, 1994, 50, 11499-11508. 

In 1985, Campbell et al. [58] employed a Dieckmann condensation strategy to the synthesis of pulvinones. By this route, Campbell prepared tetronic acid 61 that can be either transformed to phosphorane 62 and utilized in Wittig reactions or condensed with arylaldehydes that can afford pulvinones after dehydration. The first route led Steglich s group in 2000 to the total synthesis of aurantricholides A (65) and B (66), two minor pigments of toadstool Tricholoma aurantium [59], whereas... 

Z- Configuration is typical of the majority of a-aryl(hetaryl)-/V-alkylaldo-nitrones. The isolation of -isomers in the condensation of aromatic aldehydes with iV-j3-]ihenyletli Tliydroxylamine has been described (155). The synthesis of a, N -diary lnitrones gives best results if acidic catalysis is employed (156), or when clay is used as a catalyst (157). Significant reduction of reaction time and increase in the yields of nitrones can be achieved if microwave irradiation is used (158, 159). On the basis of polymeric arylaldehydes, the synthesis of polymeric a,-diarylnitrones has been described (160). 

Condensation of /3-phenylpropionamides with arylaldehydes, and then cyclization to l-aryl-2-benzazepin-3-ones (Pictet-Spengler reaction) is successful in PPA. The reaction fails, however, with aliphatic aldehydes. An analogous condensation between /3-(m-hydroxyphenyl)propylamine and then cyclization in hot butanol yields l-aryltetrahydro-2//-... 

The apparent fickleness of the acyl-pyrroles and -indoles in their reaction with carbanions to form new C—C bonds arises from the contribution made by the zwitterionic structure, e.g. (410b), to the resonance hybrid and the choice of the reaction conditions is critical for a successful nucleophilic reaction. Thus, formyl-pyrroles and -indoles do not normally undergo the Cannizzaro reaction nor do they form stable cyanohydrins or undergo benzoin-type reactions. However, surprisingly, 2-formylpyrrole reacts with arylaldehydes in the presence of potassium cyanide to yield (428), which is easily oxidized to (429) (B-77MI30505). It is noteworthy that the presence of an ester substituent adjacent to the formyl group modifies the mesomeric interaction to such an extent to allow the formation of (430) in low yield, as a result of an initial benzoin-type self-condensation (Scheme 76) (68BSF637). 

Aryl-l,4-dihydropyridines, which are easily convertible to 4-arylpyridines, are usually prepared accorchng to the method of Hantzsch starting from arylaldehyde, 1,3-dicarbonyl compound and ammonia in a one-step reaction A variation of the Hantzsch synthesis uses enaminones instead of -dicarbonyl derivatives (for another variant, see Section ILA.l.e). Here the method consists of a condensation of two enaminone molecules and one molecule of aromatic or aliphatic aldehyde to give 1,4-dihydropyridines (equation 14). Various dihydropyridines have been synthesized by this rnethod ". Enaminonitriles can be cyclocondensed in the same manner (equation 15). 

Condensation of triamine (171) with arylaldehydes in dimethylformamide at room temperature affords 4-amino-6-aryl-l,5-dihydroimidazo[4,5-c][l,2,6]thiadiazine 2,2-dioxides (177) in 63-95% yield. The reaction is also successful with ethanal, but proceeds in lower yield (45%) <87H(26)3123). Studies in the late 1980s, revealed that under anhydrous conditions and with electron rich aldehydes, mixtures of the imidazo[4,5-c]-thiadiazine dioxides (177) and pyrazino[2,3-c]thiadiazine dioxides (180) are produced <88JHC89i, 89MI616-01). The latter products arise by electrocyclization of the bis-anils (178), formed by condensation of the triamine with two equivalents of aldehyde, followed by... 

With arylaldehydes in a type of Knoevenagel reaction, 2-alkyl-4,5-dihydrooxazoles 1 yield condensation products 2, which on acid hydrolysis give 2-alkyl-3-arylpropenoic acid 3 ... 

---