Aldehydes a-methoxy

Condensation of the carbanion of optically active p-tolyl p-tolylthiomethyl sulphoxide 380 with benzaldehyde and phenylacetaldehyde produces the corresponding sulphoxides 432 which are converted into optically active a-methoxy aldehydes 433 and alcohols 434 with enantiomeric excess of 70% and 46%, respectively506,507 (equation 259). 

Quite recently, the addition of methoxy anion to the optically active styryl sulfoxide 314 was found to give a mixture of diastereo-meric dithioacetal mono-iS-oxides 315, which were converted to the optically active a-methoxy aldehyde 316, having 59.6% optical purity (316). 

Chiral a-methoxy aldehydes.2 The anion of 1 undergoes 1,2-addition to bcnzaldehyde in quantitative yield. The adduct can be methylated under phase-transfer conditions and then reduced3 to give the dithioacetal 2, from which the aldehyde 3 is liberated by reaction with I2 and NaIlC03.4 The optical yield of 3 is >70%. 

Chiral a-methoxy aldehydes. The anion ot (S)-l reacts with benzoyl chloride to give two products (2) in the ratio 99 1. L1A1H4 reduction of 2a, 2b gives only two a-tolylthio-p-hydroxy sulfoxides (3a,b) rather than the expected four diastereomers. Evidently the LiAlHi reduction is highly regiospecific. Either 2 or 3 can be separated by crystallization or chromatography and converted into optically pure a-methoxy aldehydes (4, equation 1). 

Scheme 10 summarizes what appears to be a highly stereoselective addition to an a-methoxy aldehyde. The (Z)-lithium enolate (173), formed from the enone by reaction with lithium hexamethyldi-silazane, reacts with benzaldehyde to give syn and anti aldols in a ratio of 8 1. Reaction of (173) with... 

The empirical formula contains five double-bond equivalents. In the H NMR spectrum a doublet signal at Sh = 9.55 stands out. This chemical shift value would fit an aldehyde flinction. Since the only oxygen atom in the empirical formula is thus assigned a place, the methyl signal at Sh = 3.80 does not belong to a methoxy group, but rather to an /f-methyl group. 

Yamamoto et al. have reported a chiral helical titanium catalyst, 10, prepared from a binaphthol-derived chiral tetraol and titanium tetraisopropoxide with azeotropic removal of 2-propanol [16] (Scheme 1.22, 1.23, Table 1.9). This is one of the few catalysts which promote the Diels-Alder reaction of a-unsubstituted aldehydes such as acrolein with high enantioselectivity. Acrolein reacts not only with cyclo-pentadiene but also 1,3-cyclohexadiene and l-methoxy-l,3-cyclohexadiene to afford cycloadducts in 96, 81, and 98% ee, respectively. Another noteworthy feature of the titanium catalyst 10 is that the enantioselectivity is not greatly influenced by reaction temperature (96% ee at... 

Chiral tricyclic compounds have been prepared by thermal and Eu(fod)j-catalyzed cycloadditions of furanosidic a,-unsaturated aldehydes 26-29 (Figure 3.4) with cyclopentadiene (18) [31]. The diastereofacial selectivity depends markedly on the stereochemistry of the anomeric benzyloxy and methoxy groups. 

They react with aldehydes to give a-methoxy alcohols. 

The C(9)-C(14) segment VI was prepared by Steps D-l to D-3. The formation of the vinyl iodide in Step D-3 was difficult and proceeded in only 25-30% yield. The C(15)-C(21) segment VII was synthesized from the common intermediate 17 by Steps E-l to E-6. A DDQ oxidation led to formation of a 1,3-dioxane ring in Step E-l. The A-methoxy amide was converted to an aldehyde by LiAlH4 reduction and the chain was extended to include C(14) and C(15) using a boron enolate of an oxazo-lidinone chiral auxiliary. After reductive removal of the chiral auxiliary, the primary alcohol group was converted to a primary iodide. The overall yield for these steps was about 25%. 

For the Cu(OTf)2-promoted reaction between ethyl diazoacetate and cinnam-aldehyde dimethyl acetal, products 143-145 account for only 35% the total yield. C/C and C/H insertion products 151 and 152 are obtained additionally in 49 and 14% yield, respectively154). It was assumed that the copper compound acts through Lewis-acid catalysis here, just as it is believed to do when orthoesters are used as substrates 160). According to this, catalyst-induced formation of a methoxy-... 

The E-crotylboronate derivatives 28 and 75 behave similarly. As shown in Eqs. 61 and 62, these reagents were successfully tested with simple ahphatic aldehydes and benzaldehyde and provide very high levels of stereoselectivity in the formation of anti-propionate products. Although the a-methoxy derivative 75 is more diastereoselective, it provides lower enantioselectivity because it can be obtained only in 90% ee from enantiopure 28 via an Sn2 displacement that canses some erosion of the enantiomeric purity. 

The (+)- and (—)-4,5-dialkoxy-2-oxazolidinones 173 and 174 prepared through the 5-bromo-4-methoxy- derivatives serve as reliable chiral synthons for the preparation of a wide variety of optically active a-amino acids 176 and a-amino aldehydes 177 (Fig. S.TS)." ... 

Properties. Vanillin is a colorless crystalline solid mp 82-83 °C) with a typical vanilla odor. Because it possesses aldehyde and hydroxyl substituents, it undergoes many reactions. Additional reactions are possible due to the reactivity of the aromatic nucleus. Vanillyl alcohol and 2-methoxy-4-methylphenol are obtained by catalytic hydrogenation vanillic acid derivatives are formed after oxidation and protection of the phenolic hydroxyl group. Since vanillin is a phenol aldehyde, it is stable to autoxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxyl group and by aldol condensation at the aldehyde group. Several of these derivatives are intermediates, for example, in the synthesis of pharmaceuticals. 

The ozonolytic cleavage of cycloalkenes in the presence of methanol produces a chain with an aldehyde and a methoxy hydroperoxide group at the termini.8 The unsymmetrical ozonolysis product is manipulated in several... 

Preparation of a Boc-Protected a-Amino Aldehyde via Reduction of the Corresponding Boc-Protected a-Amino Acid W-Methoxy-A-methylamide General Procedure 126 ... 

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