Aldehydes substitutes

Dinitrophenyl-hydrazine has been successfully employed in the analysis of simple aldehydes, substituted aldehydes, glyoxal and gluteraldehyde (43-45), all the isomers of the C3 to C7 aliphatic ketones (44,45) and in the determination of formaldehyde in tobacco smoke (46). 

L-Rhamnosone was prepared by the action of hydrochloric acid on L-rhamnose phenylosazone9 and was identified by reconversion to the osazone. This method was later employed186 as a stage in the synthesis of the ascorbic acid analog, L-rhamnoascorbic acid. The benzaldehyde decomposition of the osazone gave a low yield of osone93 and o-nitrobenzaldehyde was not a satisfactory aldehydic substitute. 

Figure 3.23 Dynamic combinatorial assembly of DNA primers on a template through imine formation between 5 -amino-substituted and 3 -aldehyde-substituted DNA strands.

In contrast to wild-type BFD, BAL accepts aromatic aldehydes substituted in the ortho position as well. Only a few aromatic aldehydes, such as pyridine 3- and 4-carbaldehyde as well as sterically exceedingly demanding aldehydes, resulted either in very low yields or in no benzoin condensation at all [62]. Moreover, mono- and dimethoxyacetaldehyde are good substrates for BAL, leading to highly functionalized enantiopure hydroxypropiophenone derivatives (Scheme 2.2.7.22) [63]. 

All aromatic aldehydes and heterocyclic aldehydes substituted with strong electron-withdrawing groups react cleanly with sulfur tetrafluoride at elevated temperatures, preferably in the presence of hydrogen fluoride, to give good yields of the respective difluoromethyl derivatives typical examples are given by the formation of 15. 

Some ester- or aldehyde-substituted bicyclo[2.2.2]oct-2-ene and bicyclo[2.2.1]hept-2-ene systems (25) have been shown to undergo nitrosation adjacent to the carbonyl group followed by [3,3]-sigmatropic rearrangement to give oxazine products (26).23 Stereodeflned monoprotected allylic 1,2-diol (27) and its diastereomer have been ( ) converted into stereodeflned propenylimidazolidinone (30) and its diastereomer by... 

The stereochemical outcome can be rationalized by considering the approach of the aldehyde to the preferred conformation of the allylindium. The approach of the aldehyde is postulated to be in antiperiplanar to the OPG group as for the Felkin-Anh model. The allylindium prefers to adopt the conformation 12 rather than 13, where the 1,3-allylic strain with R is minimized and the steric interaction with the aldehyde is also reduced (Scheme 18). The facial selection with respect to the aldehyde is determined by the aldehyde residue (R ) to occupy in the least sterically demanding position, away from the substituted allylic carbon. The carbonyl allylation then proceeds via a six-membered chairlike transition state, in which the aldehyde substitutent attains an equatorial position, to afford the 1,4-syn product. 

The addition of tributylstannyllithium to the carbonyl group of various a-substituted aldehydes is accompanied by asymmetric a-induction8. The extent depends only on the relative sizes of a-substituents. The tributylstannyl anion exhibits much the same stereoselectivity as unhindered Grignard reagents (for 2,3-dimethylbutanal d.r. 3 1 and 2.5 1, respectively). Stereoselectivity is improved with aldehydes substituted at the /(-position by oxygen. For example, when a-methyl-/i-(benzyloxy)methoxypropanal is treated with tributylstannyllithium in tetrahydrofuran, a mixture of diastereomers is formed, the ratio of which varies from 5 1 at — 78°C to8 l at — 119"C8. 

N,N-Dialkylformamide or ethyl formate" and Grignard reagents have been used with some success however, the former reaction is complicated and frequently produces tertiary amines as the chief product, and the latte forms secondary alcohols by further reaction of the aldehyde. Substituted benzaldehydes have been prepared from aryllithium compounds and N-methylformanilide in good yields. ... 

In Section 3.5.2 we described the highly enantioselective addition of dialkylzinc to achiral aldehydes catalyzed by chiral 1,2-disubstituted ferrocenyl amino alcohols, which shows high stereoselectivity even in the alkylation of a-branched aliphatic aldehydes. In order to further develop the characteristics of our catalysts, the ethylation of aldehydes substituted with an a-thio- and seleno group was investigated. 

Cinnamic Aldehyde.—The other aromatic aldehyde which we shall mention is cinnamic aldehyde. It contains the aldehyde group in the side chain and not in the benzene ring, and is thus an aliphatic aldehyde substitution product of benzene. The aliphatic side chain is also an unsaturated chain. Its formula is CeHs—CH=CH—CHO, and it may be considered as beta-phenyl acrylic aldehyde. As an aldehyde it yields by oxidation an acid, viz., beta-phenyl acrylic acid or, as it is commonly known, cinnamic acid. The aldehyde is found in oil of cinnamon obtained from cinnamon bark, hence its name and the name of the acid. The most important synthesis is by the condensation of benzaldehyde and acetaldehyde, as follows ... 

Actually, a steric congestion effect was also manifested with other substrates. For example, with aromatic carboxylic acids or aldehydes substituted on the... 

In the nucleophilic addition reactions of amines to substituted aromatic aldehydes where acid catalysis is required, the use of EAN seems to be convenient. The EAN can take part in an acid-base equilibrium with the aromatic aldehydes substituted by electron-withdrawing groups. The imine products from the selected aldehydes could be obtained, confirming the dual behaviour of EAN as Brbnsted acid and potential nucleophile in these type of processes (Fig. 13.7). 

The addition reaction of fert-butyl thioacetate-derived silyl ketene acetal produces the corresponding aldol adducts in 84% yield and up to 96% enantiomeric excess (Eq. 16). The enantioselectivity of the products was observed to be optimal with toluene as solvent the use of the more polar dichloromethane consistently produced adducts with 10-15% lower enantiomeric excess. The bulkier ferf-butylthioacetate-derived enol silane was found to lead to uniformly higher levels of enantioselectivity than the smaller S-ethyl thioketene acetal. This process is impressive in that it tolerates a wide range of aldehyde substrates for instance, the aldol addition reaction has been successfully conducted with aldehydes substituted with polar functionaUty such as N-Boc amides, chlorides, esters, and 0-benzyl ethers. A key feature of this system when compared to previously reported processes was the abiUty to achieve high levels of stereoselectivity at 0 °C, in contrast to other processes that commonly prescribe operating temperatures of -78 °C. 

Figure 5.1 lists a number of auxiliaries for asymmetric allyl addition to aldehydes. Substituted allyl boron compounds have also been used in reactions with achiral aldehydes. Table 5.1 lists several examples of 2- and 3-substituted allyl boron compounds, and the products derived from their addition. Note that for the E- and Z-crotyl compounds, the enantioselectivity indicated is for the isomer illustrated. In some cases, there was more than one of the other three possible isomers found as well. 

Fig. 10.3-5 Tyrosine modification using a when proteins are treated alone with either three component Mannich-type reaction. component, (b) The reaction conversion is (a) Aldehydes and anilines condense to listed for a number of anilines and aliphatic form imines in situ, which react with tyrosine amines using a-chymotrypsinogen A as the residues through an electrophilic aromatic substrate and formaldehyde as the aldehyde substitution reaction. No reaction occurs component.

A notable feature associated with some of these methods is that high yields of a,6-unsaturated esters are obtained even with rather sensitive aldehydes substituted by unprotected hydroxy-, nitro-, or keto-groups. Exceptionally sensitive aldehydes which may even defy isolation can be generated and trapped in situ by carrying out a Swern oxidation of the corresponding alcohol at -78 C and then adding a stabilized phosphorane [e.g. (176)] (Scheme 15). Remarkably high yields can be obtained in the... 

Enantiomeric forms of carboxy-, acetyl-, hydroxymethyl- and aldehyde-substituted cyclopentadienyl and benzyl complexes of Cr, Mn, and Fe are separated on Chiralcel OC, OD, OT, and OB columns (A —220 tun) using hexane/IPA and hexane/ethanol mobile phases (at the 1-3% level). Better peak resolution was obtained when ethanol was used in the modifier [616]. For both modifiers, resolution increases rapidly as percent organic modifier decreases. Capacity factors of 5-20 were obtained depending upon the sol vent/solute combination chosen. 

The use of a chiral aldehyde to generate a chiral imine is somewhat more difficult than it might first appear. The chiral center should be close to the aldehyde carbonyl, but these are notorious for their facile enolization. Further, it is imperative that the derived imine does not also enolize to form the corresponding enamine. In general, aldehydes substituted with a-nitrogen or a-oxygen substituents have been found suitable, while successful applications of a-alkyl aldehydes have been less common. Aldehydes with chiral a-nitrogen substituents are readily derived from a-amino acids, and N-... 

As mentioned already, achiral molecules can also be employed to obtain chiral surfaces. Wang et studied the self-assembly of an achiral aldehyde-substituted oligo (p-phenylene vinylene) (OPV3-CHO) at the air/graphite interface (Figure 12a) focusing on the structure and... 

---