Vinylogous donors

Here the hapten (Scheme 2) is a 13-diketone, which incorporates structural features of both reactants - ketone donor and aldehyde acceptor (see below, Scheme 3) - in the aldol reaction of interest. In favorable cases the hapten reacts with the primary amino-group of a lysine residue in the complementary-determining region of an antibody to form a Schiffbase 5, which readily tautomerises to the more stable vinylogous amide 6. 

The concept of captodative substitution implies the simultaneous action of a captor (acceptor) and a donor substituent on a molecule. Furthermore, in the definition of Viehe et al. (1979), which was given for free radicals, both substituents are bonded to the same or to two vinylogous carbon atoms, i.e. 1,1- and 1,3-substitution, and so forth is considered. One might, however, also include 1,2-, 1,4-,. .. disubstitution, a situation which is more often referred to as push-pull substitution. Before discussing captodative substituent effects it might be helpful to analyse the terms capto and dative in more detail. 

I 74 Rhodium(ll)-Stabilizecl Carbenoids Containing Both Donor and Acceptor Substituents Tab. 14.11 Tropane formation versus vinylogous reactivity. 

The iron catalysis of vinylogous Michael reactions is not only restricted to dimerizations. The y-donor 46b can be converted with MVK (41a) to give the 1,7-dioxo-constituted product 49 when the catalyst is Fe(III) (Scheme 8.21) [75]. If NaOMe in MeOH is applied as the catalyst, reaction of the dienolate of donor 46b in the a-position with acceptor 41a proceeds via a normal Michael reaction and 1,5-dioxo-constituted product 50 is obtained. 

In hemicyanine dyes one of the charge-carrying terminal atoms of the methine chain forms part of a heterocyclic ring. The lowest vinylogous hemicyanine dyes (cyclomethine dyes) do not contain a methine chain, and the donor and acceptor groups are in the same ring system. 

A C(6) donor substituent exerts a similar enhancing efiect on the rate of the Claisen rearrangement, though somehow less pronounced than the rate-accelerating effect of the 2-silyloxy substituent (approx. 1.4 kcal mol" ). As Curran and coworkers reported, " this vinylogous anomeric effect of the C(6) donor substituent is especially effective in glycal systems. The energy of the TS is decreased by assist-... 

The electrochemical properties of the first highly conjugated vinylogous 72 covalently attached to C6o-fullerene and determined by CV in solution revealed the electroactive character of both donor and acceptor moieties. Thus, the 7t-extended donor fragment showed a two-electron single wave due to formation of a stable dicationic species in contrast to the behavior of TTF itself and its derivatives, which formed stable radical cations <1997JOC5690>. 

The dialdehyde 150 was condensed with malononitrile to give the donor-acceptor compound 151 <20020L2581>. Condensation with different phosphoranes and phosphonates gave the dendralene-type vinylogs of tetrathiafulvalene 50-52 and the donor-acceptor compound 152 <20020L2581>. 

Allylic Sources Ambident Nucleophiles Better Donors Increase Reactivity Vinylogous Allylic Sources Allyiic Alkyne Sources... 

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