Reagents aldehydes

Classical examples of this type of reaction are the various dimethylaminobenz-aldehyde reagents (q.v.) and vanillin-acid reagents, of which one, the vanillin-phosphoric acid reagent, is already included in Volume 1 a. The aldol condensation of estrogens is an example for the reaction mechanism (cf. Chapter 2, Table 6). According to Maiowan indole derivatives react in a similar manner [1]. Longo has postulated that catechins yield intensely colored triphenylmethane dyes [2]. 

Aldehyde Reagent Reaction temperature (°C) Product Yield (%)... 

With chiral aldehydes, reagent approach is generally consistent with a Felkin model.163 This preference can be reinforced or opposed by the effect of other stereocenters. For example, the addition of allyl stannane to l,4-dimethyl-3-(4-methoxybenzyloxy)pentanal is strongly in accord with the Felkin model for the anti stereoisomer but is anti-Felkin for the syn isomer. 

Fig. 10.2. Structures of complexed aldehyde reagent (a) and transition structure (b) for enantios-elective catalysis of the carbonyl-ene reaction by BINOL-Ti(IV). Reproduced from Tetrahedron Lett., 38, 6513 (1997), by permission of Elsevier.

Scheme 41. Biomimetic synthesis of chelerythrine (205) and fagaridine (238) via the enamide aldehyde. Reagents a, B2H6 b, H202, NaOH c, PCC d, T1(N03)3, MeOH e, HC1 f, LAH g, MeOH h, NaBH4 i, p-TsOH, toluene j, I2, EtOH.

Scheme 44. Biomimetic synthesis of corynoline (254), 11-epicorynoline (257), and their analog via enamine aldehydes. Reagents a, LAH b, Me2SC>4. c, KOH d, T1(N03)3, MeOH e, NaBH4 f, HC1 g, NaBH3CN.

By far, the two most popular fezs-aldehyde reagents are formaldehyde and glutaraldehyde. 

Roush reported another tartrate boronate, (E )-y-[(menthofuryI)-dimethyl silyl]-allylboronate 130, for untz -a-hydroxyallyation of aldehydes. Reagent 130 can be obtained from commercially available menthofuran, which was selected... 

The second issue is the slow release in the body of the cross-linking aldehydic reagents used to cross-link and stabilize the gelatin microparticles. This will occur slowly in vivo as the gelatin matrix itself dissociates and goes into solution. However, the effect of low level, slow, localized, release of glutaraldehyde over a period of time has not been evaluated clinically and the issue remains open for discussion. 

Numerous bis-aldehyde reagents have been used for the conjugation of biomolecules. Nearly every small organic compound containing two aldehyde groups has been at... 

Fig. 5.14 Electrochemical carboxylation of aldehydes. Reagents and conditions divided flow cell, Nation membrane, BDD/Si electrodes, NBu4+BF4 in DMF, 20-25°C, 0.6 A dm-2, 5h, 27% yield in rac-28 at 88% conversion of 27...

An interesting consideration relating to the influence of acidity in the reaction medium is derived from the comparison between the conditions adopted for the synthesis of the P-aminoketoncs 44 and 45, and tho.se required for the analogous derivatives that lack the carboxy group. Whereas the latter compounds are prepared under the. severe conditions of type A (Table 6), both the syntheses of 44, employing glyoxal as aldehyde reagent,and that of 45, which is prepared from 3-benzoyl propionic acid, take place readily under mild conditions (type B or C). 

The selection of aldehyde reagent in Mannich synthesis may be also dictated by the presence in the aldehyde moiety of groups available for subsequent reactions, such as haloalkyl (chloromethyl, etc.) or acetal groups (Refs. 158 and 163 in Table 3). 

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