Aliphatic or aromatic aldehyde

SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

The method can be used to prepare a number of a-aminonitriles from aliphatic or aromatic aldehydes and ketones and secondary aliphatic amines.4... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

Enzyme preparations from liver or microbial sources were reported to show rather high substrate specificity [76] for the natural phosphorylated acceptor d-(18) but, at much reduced reaction rates, offer a rather broad substrate tolerance for polar, short-chain aldehydes [77-79]. Simple aliphatic or aromatic aldehydes are not converted. Therefore, the aldolase from Escherichia coli has been mutated for improved acceptance of nonphosphorylated and enantiomeric substrates toward facilitated enzymatic syntheses ofboth d- and t-sugars [80,81]. High stereoselectivity of the wild-type enzyme has been utilized in the preparation of compounds (23) / (24) and in a two-step enzymatic synthesis of (22), the N-terminal amino acid portion of nikkomycin antibiotics (Figure 10.12) [82]. 

Many known color reactions involve electrophilic substitution at an electron-rich aromatic or heteroaromatic (cf. 4-(dimethylamino)-benzaldehyde - acid reagents and vanillin reagents ). Here aliphatic or aromatic aldehydes react in acid medium to yield polymethyne cations which are intensely colored di- or triarylcarbenium ions [4, 10]. 

Aliphatic or aromatic aldehydes RCHO can be transformed, in situ, via their iminium iodides, on reaction with enamines of ketones, to give /9-aminoketones. Thus, 4-methoxybenzaldehyde reacts with dimethylammonium chloride, triethyla-... 

Similarly, a high-density brine, useful as a drilling fluid for deep wells, is made corrosion resistant by adding an aliphatic or aromatic aldehyde and thiocyanates [817]. The aldehyde can be reacted with a primary amine before use. 

These authors also prepared novel epoxy-bridged cyclooxaalkanones in this process, the carbonyl group always acts as 1,3-dipolarophile, even if one employs ct,(3-unsaturated aldehydes. Thus, reaction of 6/2-16 with aliphatic or aromatic aldehydes 6/2-17 in the presence of catalytic amounts of rhodium acetate gave 6/2-18, regioselectively. With the a, 3-unsaturated aldehydes 6/2-20, only cycloadducts 6/2-21 were obtained using the diazo compound 6/2-19 as substrate (Scheme 6/2.3) [191]. 

Trimethylsilyl trichloroacetate is a useful reagent for the A-trimethylsilylation of amines284. The combined action of primary aliphatic or aromatic amines and trimethylsilyl cyanide on aliphatic or aromatic aldehydes yields a-amino nitriles (equation 93)285,286. 

The reduction of different aliphatic or aromatic aldehydes or ketones 15 was easily achieved using the combination of dihydrated nickel(II) chloride, lithium and a catalytic amount of naphthalene (16%) or DTBB (8%) in THF, yielding the corresponding alcohols without (534) or with (535) deuterium labelling in 57-86% yield. For imines 536, the same process afforded the corresponding amines 537 or deuterio amines 538 in 54- >95% yield . 

Dealing with the synthesis of dihydropyridopyrimidinones, the procedure was quite similar to the precedent, involving 2,6-diaminopyrimidin-4(3//)-one as enaminocarbonyl partner, various 1,3-dicarbonyl derivatives, and either aliphatic or aromatic aldehydes in water under microwave irradiations (Scheme 11). Interestingly, the guanidine system was unreactive, and a library of tri- and tetracyclic dihydropyridopyrimidinone derivatives was chemoselectively synthesized in high yields and short reaction times from this environmentally friendly procedure. 

Cannizzaro Reaction The formation of an acid and an alcohol through the base-catalyzed disproportionation of an aliphatic or aromatic aldehyde with no a-hydrogen atoms. 

In the reactions of 4-amino-l-azadienes 295 with esters of glyoxylic acid, chemoselective cyclization occurred with displacement of the amino group NHR, and 2/7-1,3-oxazine-2-carboxylic acid derivatives 296 were formed in high yields instead of the corresponding 1,2-dihydropyrimidines usually obtained in the reactions of 295 with aliphatic or aromatic aldehydes (Equation 28) <1996T3095>. 

When 2-aza-3-silyloxy-l,3-diene 336 was heated with aliphatic or aromatic aldehydes in toluene, stereoisomeric tetrahydro-l,3-oxazin-4-one derivatives 200 and 337 were obtained without Lewis acid catalysis (Equation 34). The cycloaddition proved to be highly diastereoselective in favor of the OTr/o-adducts, leading to the >-isomers 200 as the main products <1999TL7079, 2002S2043>. 

The 7V,N-dimethylcarbamate 351, when reacted with LDA and aliphatic or aromatic aldehydes, afforded surprisingly ortho-rearranged products 353 (Scheme 109) (87JHC1487). 

The reaction of diethyl cyanomethylphosphonate in the presence of A1203 with aliphatic or aromatic aldehydes in the absence of solvent results mainly in the product of Knoevenagel reaction (equation II). 

The Pseudomonas fluorescens KdgA was shown to accept several polar-sub-stituted aldehydes, albeit at rates much lower ( < 1%) than the phosphorylated natural substrate 12 (Table 3) [137]. Simple aliphatic or aromatic aldehydes were not converted. Synthetic utility and high stereoselectivity with unnatural substrates were demonstrated by conversion of both the D-configurated glycer-aldehyde (d-15) and lactaldehyde (d-16) to form the respective (4S)-configurated adducts 17 and 18 at the mmol scale. 

The direct interaction of benzyl carbonyl compounds 38 and 48 with aromatic aldehydes in the presence of PPA or AC2O + HC104(86KGS125 87TH1), or with acetals or acylals of aliphatic or aromatic aldehydes in the presence of triphenylmethyl perchlorate (73KGS881 75ZOR1962), gives rise to benzo[c]pyrylium salts 62 in yields of 15-70 %. 

Wittig reactions.1 Potassium carbonate can function as a solid-liquid transfer catalyst for Wittig reactions of aliphatic or aromatic aldehydes with alkyltriphenyl-phosphonium bromides in dioxane containing a trace of water. K2CO3 is superior to NaOH because it does not catalyze aldol condensation. As expected, the (Z)/(E) ratio is 70 30. 

An alternative strategy for preparation of monoacylated 1,2- and 1,3-diols is oxidative deavage of cyclic acetals prepared from a diol and an aliphatic or aromatic aldehyde (Scheme 10.7). For this purpose the required acetal does not need to be isolated, but can be generated in situ [25]. Acetals prepared from strongly electrophilic aldehydes, for example nitrobenzaldehydes, will, however, usually be difficult to oxidize (and to hydrolyze). 

The acid-mediated condensation of 2-naphthol with aliphatic or aromatic aldehydes can proceed under solvent-free conditions or in dichloroethane to give 14-alkyl/aryl-14//-dibcnzo[tf1/]xanthenes 167 in excellent yield (Equation 78) <2005SL955>. Sulfamic acid can also effectively catalyze the condensation of 2-naphthol with aromatic aldehydes either at 125 °C or under microwave irradiation to yield 14-aryl-14//-dibenzo[tf,/]xanthcncs in high yield (92-96%) <2005TL8691>. 

Fig. 17.17. Sodium chlorite oxidation of aliphatic or aromatic aldehydes to form a carboxylic acid. The extra additive destroys the reduction product of the oxidant, i.e., sodium hypochlorite or hypochloric acid.

A modification of the excellent method of R. Weidenhagen [Ber., 69, 2263 (1936)] for the preparation of 2-substituted benzimidazoles directly from an aliphatic or aromatic aldehyde and an o-diamine. 

Asymmetric hydrocyanation of aldehydes.3 This reaction can be effected by reaction of aliphatic or aromatic aldehydes with cyanotrimethylsilane and an optically active reagent (1) derived from (2R,3R)-tartaric acid, and dichlorodiisopro-poxytitanium(IV). The actual chiral reagent may be 2, shown by H NMR to be... 

Reaction of RCHO with CJfCH=CHCH1Cl. This reaction can be regio-selective and f/ireo-selective when mediated by Sn and Al. The reaction of benz-aldehyde with cinnamyl chloride provides the anfi-homoallylic alcohol as the only detectable product. This diastereoselectivity obtains generally with aliphatic or aromatic aldehydes. The reaction with enals under the same conditions provides only the 1,2-adducts, again with anti-selectivity (equation I). The reaction of 2-phenylpropanal with 1 provides a mixture of homoallylic alcohols in the ratio 3 1, with anti-selectivity at the C—C bond formed in the reaction (equation II). 

Iodonium enolates 293, formally derived from unactivated monoketones, can be generated in situ by the action of lithium ethoxide on (Z)-/3-acetoxyvinyhodonium salts 292 (97JA11598, 98TL5569, 99JOC3181). When aliphatic or aromatic aldehydes are present in the reaction... 

The reactions of mercaptothiolacetic acid with aliphatic or aromatic aldehydes lead to the formation of l,3-dithiolan-4-one derivatives (291) (73JOC3953). 

Note The pyrazinylsulfonyl grouping has been employed as a leaving group in the formation of unsaturated aliphatic compounds and aliphatic or aromatic aldehydes.297 302 308,319... 

The joint action of pyridine and thionyl chloride on aliphatic or aromatic aldehydes RCHO results in 1-chloromethylpyridinium chlorides 272, which react with ethyl jS-aminocrotonate to give 1,4-dihydropyridines 273 (equation 113). The reaction constitutes a modified Hantzsch synthesis it has the advantage over the latter that it proceeds under milder conditions and gives better yields138. The dihydropyridine 273 (R = H) is also readily obtained from ethyl / -aminocrotonate and formaldehyde in the presence of catalytic amounts of 4-(dimethylamino)pyridine139. 

Interestingly, the mild reaction conditions of the CIR are fully compatible with the Stetter reaction. As a result a sequence of transition metal, base and organoca-talysis can be easily conceived. Upon CIR of electron-deficient (hetero)aryl halides 11 and (hetero)aryl propargyl alcohols 12, and after subsequent addition of aliphatic or aromatic aldehydes 92 and catalytic amounts of thiazolium salt 93 1,4-diketones 94 are obtained in moderate to excellent yields in a one-pot procedure (Scheme 50) [259, 260]. For aromatic aldehydes the catalyst precursor of choice is 3,4-dimethyl-5-(2-hydroxyethyl) thiazolium iodide (93a) (R = Me), and for aliphatic aldehydes 3-benzyl-4-methyl-5-(2-hydroxyethyl)-thiazolium chloride (93b) (R = CH2Ph) is applied. 

Olefinic esters are obtained directly by the Knoevenagel condensation (cf. method 37) of ethyl hydrogen malonate with an aliphatic or aromatic aldehyde. 

Acylals are formed by the addition of simple anhydrides to aliphatic or aromatic aldehydes. The reaction occurs at 0-5° in the presence of boron trifluoride etherate. Yields are in the range of 65% to 81%. ... 

Single electron oxidation of the non-activated carbonyl group, e.g. in aliphatic or aromatic aldehydes, ketones and carboxylic acid derivatives, is, on the other hand, much less feasible and only a handful of methods and synthetic applications are known. Useful methods for synthetic applications are chemical modifications to lower the oxidation potentials by peripheral donor substitution and a-silylation, or redox umpolung via oxidation of the corresponding carbonyl enols or enol ethers. 

Again, a chromium-free oxidation method is employed. Sodium chlorite oxidizes aliphatic or aromatic aldehydes. In the process it forms hypochloric acid (HOCl) or sodium hypochlorite (NaOCl), which are even more reactive than sodium chlorite and therefore must be quenched in situ by the olefinic additive 2-methyl-2-butene in an acidic buffer medium. 

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