Hydroxy aldehydes cinnamic acid

The simplest synthesis of coumarins is a special case of the Perkin condensation i.e. the condensation of an aromatic aldehyde with an anhydride. ortho-Hydroxy-trans-cinnamic acids cannot be intermediates since they do not isomerise under the conditions of the reaction nor can O-acetylsalicylaldehyde be the immediate precursor of the coumarin, since it is not cyclised by sodium acetate on its own. ... 

Two mechanisms have been proposed for the Knoevenagel reaction. In one, the role of the amine is to form an imine or iminium salt (378) which subsequently reacts with the enolate of the active methylene compound. Under normal circumstances elimination of the amine would give the cinnamic acid derivative (379). However, when an o-hydroxy group is present in the aromatic aldehyde intramolecular ring closure to the coumarin can occur. The timing of the various steps may be different from that shown (Scheme 118). 

Cinnamic acid, a-(/9-HYDROXYSTYRYL)-, y-LACTONE, 43, 3 Cinnamyl bromide, 44, 32 Condensation, of aldehydes and ketones with esters to give (S-hydroxy-esters, 44, 58... 

Carbostyril.—If in the Baeyer and Drewsen synthesis cinnamic acid is used instead of cinnamic aldehyde the or//fo-amino derivative, by loss of water, yields a hydroxy quinoline known as carbostyril. 

Further steps in the synthesis of coumarin via the ortho-hydroxy benzaldehydes involve a Perkin reaction. Here, in the first instance, a cinnamic acid is obtained. The cinnamic acids are obtained more conveniently by the Wittig reaction of the aldehydes with the stable phosphoranes, Ph3P=C—COOEt. Indeed lithiation... 

Figure 16.6 Bienzymatic synthesis of (R)-4-phenyl-2-hydroxy-( )-but-3-enoic acid from cinnamic aldehyde (0.1 M) and HCN (0.5 M) in the presence of a combi-CLEA of PaHnL and NIT-104, in 50 50 DIPE-buffer pH 5.5 at r.t legend 1c 2c 3c , 4c ...

The conversion of phenylalanine, a C-6—C-3 precursor, to the C-6—C-1 unit of the Amaryllidaceae alkaloids requires the formal loss of two carbon atoms from the side chain of the amino acid as well as the introduction of at least two oxygenated substituents into the aromatic ring. The results shown in the latter part of Table III emphasize the specificity of the C-6—C-1 precursor. Benzaldehyde, -hydroxybenzal-dehyde, isovanillin, and protocatechuic acid are not incorporated to any appreciable extent into the alkaloids, while cinnamic, -hydroxy-cinnamic and caffeic acids, protocatechuic aldehyde, and 3-hydroxy-4-methoxy-i C-A-methyl-i4( ., enzylamine readily become part of the C-6—C-1 unit. 

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