Aldehydes conjugation using

These ,(i-unsaLurated ketones and aldehydes are used as reactants in conjugate additions (Section 2.6), Robinson annulations (Section 2.1.4), and in a number of other reactions that we will encounter later. Entries 8 and 9 in Scheme 2.12 illustrate... 

Figure 5.13 M2C2H can be used to crosslink a sulfhydryl-containing molecule with an aldehyde-containing compound. Glycoproteins may be conjugated using this reagent after treatment with sodium periodate to form reactive aldehyde groups.

Though some of these reactions use enolisable aldehydes, none uses enolisable Michael acceptors so the question of competition of this a reaction with extended enolisation proper has not arisen. One alternative approach uses an indium-mediated reaction of the y-brominated ester 163 with aldehydes to give either non-conjugated 165 or conjugated 166 a -products.43... 

Initially, an alternative approach to C14 methyl incorporation was explored based on asymmetric conjugate addition (Scheme 6). Aldehyde 10 was homologated to aldehyde 15 using a Wittig reaction with the ylide generated from methoxymcthyl phosphonium chloride. The unsaturated acyl oxazolidinone 17 was then formed with high -selectivity using phosphonate 16 in the presence of base and lithium chloride. Various... 

Scheme 26.7 Enantioselective conjugated addition of silanes into a, 8-unsaturated aldehydes catalyzed using copper and chiral iminium catalysts.

As described by Cordova et al., the strategy of combining transition metal-catalysed nucleophilic activation with chiral amine-catalysed iminium activation allows the enantioselective conjugate silyl addition to a,p-unsaturated aldehydes [115]. The reaction proceeds with good 1,4-selectivity and moderate enantio-selectivity when p,p-disubstituted unsaturated aldehydes are used as substrates, as exemplified in Scheme 77. The silylated products are versatile adducts that can be easily converted to protected 1,3-diols and p-functionalised esters. 

The reaction of the hydroxyl group of PEG and epichlorohy-drin allows a terminal epoxy moiety to be introduced, which can be subsequently employed for amine conjugation (Figure 2, structure 7). Similar to PEG-aldehyde, the use of PEiG-epoxide for conjugation suffers from low reactivity and lack of specificity since the formed hydroxy groups may also reart. 

FIGURE 20.30 (a) Schematic representation of surface-induced, on-site polycondensation of a Jt-conjugated polymer and (b) aromatic amine and aromatic aldehyde units used for on-site polycondensation. (Reprinted with permission from Liu, Y.F., Krug, K., Lee, Y.L., Self-organization of two-dimensional poly(3-hexylthiophene) crystals on Au(lll) surfaces. Nanoscale, 5,7936-7941,2013. Copyright 2013 American Chemical Society.)... 

The condensation of aldehydes or ketones with secondary amines leads to "encunines via N-hemiacetals and immonium hydroxides, when the water is removed. In these conjugated systems electron density and nudeophilicity are largely transferred from the nitrogen to the a-carbon atom, and thus enamines are useful electroneutral d -reagents (G.A. Cook, 1969 S.F. Dyke, 1973). A bulky heterocyclic substituent supports regio- and stereoselective reactions. 

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