Aldehyde directing effect

The /J-amino aldehyde 1. readily available from aspartic acid, is configurationally very stable. No epimerization of the stereocenter is observed upon addition of Grignard Or cuprate reagents and the transformations display relatively high levels of 1,3-asymmetric induction73. This C-3-directing effect is superimposed upon the 1,2-directing effects of the C-2-substituents (Rl). 

The powerful directing effect of bis(isopinocampheyl) allylic boranes has been put to great use in the context of several applications of double diaster-ereoselective allylations in the total synthesis of natural products. As discussed in a previous section, the Brown allylation can be exploited to overcome the stereodirecting effect of chiral a-stereogenic aldehydes, including a-aUcoxy substituted ones. Thus, the simple allylation of aldehyde 154 provides as major product the desired diastereomer needed towards a total synthesis of brasilenyne (Scheme 14). The yield and stereoselectivity is even increased to over 97 3 under the low-temperature, magnesium-free conditions described before. 

Kinetic resolution can be accomplished by addition of allyl boronates to aldehyde groups adjacent to the tricarbonyliron fragment [59]. For the synthesis of ikaruga-mycin, Roush and Wada developed an impressive asymmetric crotylboration of a prochiral meso complex using a chiral diisopropyl tartrate-derived crotylborane (Scheme 1.25) [60]. In the course of this synthesis, the stereo-directing effect of the tricarbonyliron fragment has been exploited twice to introduce stereospedfically a crotyl and a vinyl fragment. 

The direct effect of benzaldehyde on C. elegans chemotaxis kinetics was analyzed by Nuttley et al. (2001). An initial attractive response to 100% benzaldehyde was reported, followed by a strong aversion to the chemical. They determined this behavior to be mediated by two genetically separable response pathways. Initially, upon exposure, the attraction response dominates but eventually gives way to a repulsive response. Oka (2001) found that with juveniles of M. javanica, immobilization and hatching inhibition in vitro were greater with benzaldehyde and furfural than with several other essential oils. Benzaldehyde and furfural also reduced galling on tomato in pot experiments where other aldehydes were not effective (Oka, 2001). 

We can, in a qualitative way, combine the directing effects of two or more substituents. In some cases the substituents both direct to the same positions, as in the syntheses of bromoxynil and ioxynil, contact herbicides especially used in spring cereals to control weeds resistant to other weedkillers. They are both synthesized from p-hydroxybenzaldehyde by halogenation. The aldehyde directs meta and the OH group directs ortho so they both direct to the same position. The aldehyde is deactivating but the OH is activating. 

Determine the Directing Effects of a Particular Substituent 662 Aldehydes and Ketones—Nucleophilic Addition... 

Sodium chloride content is closely related to ham quality, not only because of its direct effect on taste but also because of its effect on flavour development (75). The influence of sodium chloride content on volatile compound generation could be related to its effect on lipid-oxidation reactions, enzyme activity and microbial growth. As expected, salt content affected significantly a number of compounds described previously as dry-cured odorants (Figure 1) seven aldehydes and two acids. 

Functional group-directed hydroformylation. Phosphine and phosphite moieties in olefinic substrates exert strong directing effects on the regioselectivity of hydroformylation. For example, hydroformylation of 4-(diphenylphosphino)-l-butene (32) catalyzed by Rh2(OAc)4/4PPh3 gives branched aldehyde 33, which subsequently is reduced to provide the corresponding alcohol 34 as the sole product (Eq. 16)." Under the same conditions, 1-hexene affords the linear alde-... 

Hydroformylation of substrate 130 does not show a similar directing effect and, depending on the catalyst used, gives the terminal aldehyde from which 131 or 132 are formed. 

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