Homoconjugate reactions

In dipolar aprotic solvents, the dissociation process of some acids (HA) is complicated by homo- and heteroconjugation reactions. In the homoconjugation reaction, some part of the A ions formed by the dissociation of HA [Eq. (3.18)] reacts with undissociated HA to form HA2, as shown by Eq. (3.19) ... 

Homoconjugate reactions. In comparison to cyclopropane-1,1-dicarboxylic acid, the cyclic acylal (1) shows pronounced double-bond character in reactions with nucleophiles. Thus it reacts with piperidine in benzene at 20° to give the zwitterion (2) in quantitative yield. The second reaction (II) is an example of the... 

Conjugated, cross-conjugated, and homoconjugated fluoroalkenes react with halogens to yield predominantly 1,4-adducts Results from the reactions of a series of conjugated fluoroalkenes with elemental halogens are summarized in Table 4 In nearly all cases, the fraMs-l,4-addition products are formed exclusively [Il ... 

Finally, an electrochemical reduction of bis-a-bromobenzyl sulfone to stilbene195 and a spectacular, so-called bis-homoconjugative, version of the Ramberg-Backlund reaction, which converts the a-chlorosulfone 100 into the bridged cyclooctatriene derivative 101 (equation 63)196-197, have also been published. 

In non-polar solvents many aminolysis reactions show a third-order dependence on the amine, B. This may be explained by catalysis of leaving-group departure by hydrogen-bonded homoconjugates, BH+B. Evidence for this pathway has been adduced from studies of the reactions of some nitro-activated (9-aryl oximes (7) with pyrrolidine in benzene, chlorobenzene, and dioxane, and with piperidine and hexylamine in cyclohexane. The third-order dependence on amine of the reaction of 2,6-dinitroanisole with butylamine in toluene and toluene-octanol mixtures has been interpreted in terms of a mechanism involving attack by dimers of the nucleophile. ... 

The reaction of cyclotrisilene 15 with the silylated benzenium ion [Et3Si/C6H6] results in the formation of the cyclotetrasilenylium ion 3 (see Scheme 6). The solid state structure of silyl cation 3 indicates its homoconjugative nature (see Fig. 7 and Table XIII). ... 

If a diene unit is located at an appropriate distance from the developing zwitterionic intermediate in such reactions (especially in good ionizing solvents), an intramolecular cycloaddition may intervene. This is what happens with the tetrahydrobenzo[c]thiophene 2,2-dioxide derivative (588), which leads to the bis-homobenzene (589) rapid valence isomerization of this gives the product (590) (770R(25)i). This process has been termed bis-homoconjugative rearrangement (Scheme 251). 

These results are contrary to all other observations and calculations. They reflect the danger of a careless use of bond separation reactions in connection with homoconjugated... 

The derivation of the resonance energies for 27 and 10 reveals that (a) homodesmotic reactions are well suited to compensate for the different electronic effects that hinder the calculation of pure homoconjugated resonance energies, (b) use of a homodesmotic reaction such as 24 requires the inclusion of many reference compounds, which of course can lead to considerable error progression in the calculated reaction energy, and (c) the... 

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