2-Methoxy-substituted benzaldehydes, reaction

The usual method of synthesis of methoxy substituted benzaldehyde derivatives is by formylation of the methoxy substituted benzene derivatives. The formylation is generally effected by acid catalysed electrophilic substitution reactions like the Vils-meyer-Haack reaction. When resorcinol dimethylether is formylated under these conditions, the product obtained is the derivative (2) and not (7). 

Starting from the findings of the racemic cross-benzoin condensation [66], and assuming that aldehydes not accepted as donor substrates might still be suitable acceptor substrates, and vice versa, a mixed enzyme-substrate screening was performed in order to identify a biocatalytic system for the asymmetric cross-carboligation of aromatic aldehydes. For this purpose the reactions of 2-chloro-(40a), 2-methoxy- (40b) and 2-methylbenzaldehyde (40c), respectively, were studied with different enzymes in combination with benzaldehyde (Scheme 2.2.7.23) [67]. The three ortho-substituted benzaldehyde derivatives 40a-40c were... 

The reaction is association controlled. This implies that there is no electrophilic assistance and the incoming enolate simply behaves as an ion pair. The cation remains bound to the enolate because (a) its basicity is increased by the presence of the methoxy group (the HOMO energy of a simple enolate is a + 0.682/ , whereas its methoxy substituted derivative is a + 0.564/ ), and (b) the presence of the phenyl group lowers the basicty of the benzaldehyde.56 The cryptand accelerates the reaction because it activates the enolate without deactivating the carbonyl functionality. 

In general, the Perkin reaction is limited to aromatic aldehydes. The activity of substituted benzaldehydes in the Perkin reaction is similar to the trends observed in other reactions involving the carbonyl group. A halogen (28) or nitro (34) group in any position increases the rate of reaction and the yield a methyl group (26) in any position decreases the rate and yield, and this effect falls off in the order ortho > meta > para A methoxy group in the ortho position (30) has a small favorable influence, but in the para position (32) it has a definite unfavorable effect on the rate and yield. 

The kinetics of oxidation of substituted mandelic acids (a-hydroxyphenylacetic acid) in sulfate and mixed perchlorate/sulfate solutions are the subject of the four reports from Calvaruso et al. (1981a, b) and Arcoleo et al. (1977,1979). The oxidation reaction yields (substituted) benzaldehydes upon decarboxylation of mandelic acid. The oxidation of the p-nitro and p-methoxy derivatives in sulfuric acid proceeds without significant complex formation. The authors conclude that the reaction proceeds through two reactive Ce(IV) species,... 

Ruthenium(II)-mediated oxidative annulation reaction of benzoic acids and cyclopropylarylethynes furnishes a mixture of 3- and 4-cyclopropyl substituted isocoumarins (130BC142).A facile one-pot synthesis of4-aryl-isocoumarins involves an acidic hydrolysis of ( -2-(l-aryl-2-methoxy-ethenyl)benzaldehydes with HBr and subsequent oxidation with PCC (13HCA2173). 

Substituent effects have been compared in 4-substituted benzaldehydes versus 4-substituted (phenylethynyl)benzaldehydes, 4-X-C6H4-C=C-4-QH4-CHO. For example, changing a cyano substituent to methoxy in the former causes a 54-fold decrease in the rate of an aldol reaction, whereas the factor was only 1.4 in the latter series. 

The use of oxazolines in aromatic substitution is a valuable synthetic tool.2 The o-methoxy- or o-fluorophenyloxazoline reacts readily with a variety of organofithium or Grignard reagents to displace only the ortho substituent. In this fashion a number of ortho-substituted benzoic acids, benzaldehydes, and unsymmetrical biphenyls are accessible. The reaction takes place under very mild conditions, usually at or below room temperature, and thus allows a number of other sensitive groups to be present. 

The starting materials, frans-3,4-methylenedioxycinnamyl alcohol (61a) and frans-2-methoxy-3,4-methylenedioxycinnamyl alcohol (61b) were prepared from the corresponding benzaldehyde via substituted ethyl cinnamate by means of the Horner-Emmons reaction and lithium aluminium hydride reduction. Condensation of compound (61 a) or (61 b) with compound (47) gave compound (62a) or (62b), respectively, followed by ring closure to afford compound (63a) or (63b). Intramolecular Diels-Alder reaction of compound (6 2) led to the formation of the aromatized compounds as by-product in both cases. Moreover, in the reaction of... 

Reactions suitable for the kinetics aiming at the purpose mentioned above needs to satisfy one condition. The TST must be valid for a fairly wide range of pressure and temperature. Furthermore it is desirable that the reactant can be generated in situ and the reaction can be followed spectroscopically to obtain reliable rate constants. As the first set of reactions, thermal ZfE isomerization of three N-benzylideneanilines (benzaldehyde anUs), i.e. N-[4-(dimethylamino) benzylidene]-4-nitroaniline (DBNA), N-[4-(dimethylamino)benzylidene]-4-ethoxy-carbonylaniline (DBEA), and N-[4-(dimethylamino)benzylidene]-4-bromoaniline (DBBA), and two push-pull substituted azobenzenes, i.e. 4-(dimethylamino)-4 -nitroazobenzene (DNAB) and 4 -(dimethylamino)-2-methoxy-4-nitroazobenzene (DMNAB) as shown in Scheme 3.2 were selected. 

---