Dissonant relationships

Another application of this strategy is the construction of cyclic systems bearing 1,4-dissonant relationships. For example, the synthesis of the hasubanan alkaloid ring system 35. reported in 1972 by Evans [24], involves the Diels-Alder cycloaddition of a dienyl sulphoxide 32 with an endocyclic enamine 33, followed by a [2,3]-sigmatropic rearrangement of the resulting cycloadduct 34 (Scheme 5.21). 

D.A. Evans, "Consonant and Dissonant Relationships. An Organisational Model for Organic Synthesis", UCLA Physical Organic Chemistry Seminar, 6 of May, 1971. 

In the retrosynthetic direction, consonant relationships must be disconnected, in principle, before the dissonant ones (this means that in the actual synthesis the more difficult reactions leading to dissonant relationships must be attacked in the first place. It is always less painful to deal with failures in the first stages of a synthesis). 

DISSONANT, which disconnect bifunctional dissonant relationships (1,2-D, 1,4-D and 1,6-D). 

D. A. Evans, Consonant and Dissonant Relationships An Organizational Model for Organic Synthesis , unpublished (available from D. A. Evans, Harvard University). 

Fig. 3 Dissonant relationship in morphine connectivity (a = phenol priority, b = amine priority)...

Morphine, although not particularly complex, suffers from a complete dissonant coimectivity (shown in Fig. 3) (Evans, 1972, Consonant and dissonant relationships. An organizational model, unpublished manuscript) [20], as we have previously... 

Notations 1,2-D, 1,3-C, 1,4-D, etc., refer to the relative position of the two functional groups within the carbon chain. Notice that rings, even if they have no functionality, can be classified as either consonant or dissonant depending upon whether they have an even or an odd number of carbon atoms. Table 2.4 summarises all the possibilities for bifunctional relationships as well as for rings, whether they are carbocycles or heterocycles, and whether they are funtionalised or not. 

TABLE 2.4. Consonant and dissonant linear bifunctional relationships, carbocycles, and heterocycles... 

Bifunctional systems In the case of bifunctional systems (or molecules) only two alternatives are possible the bifunctional relationships are either "consonant" or "dissonant" (apart from molecules or systems with functional groups of type A to which we have referred to as "assonant"). In the first case, the synthetic problem will have been solved, in principle, in applying the "heuristic principle" HP-2 that is to say, the molecule will be disconnected according to a retro-Claisen, a retro-aldol or a retro-Mannich condensation, or a retro-Michael addition, proceeding if necessary by a prior adjustment of the heteroatom oxidation level (FGI). 

On the contrary, if a "dissonant" bifunctional relationship is present in the system or molecule under consideration, then the synthetic problem may be much more complex and we will have to resort to some of the methods especially designed for such purposes, which will be discussed in the next Chapter. 

From the point of view of the synthesis of dissonant systems the most important finding reported by Reissig [19c] is the opening of cyclopropanes by fluoride ion-induced desilylation to give carboxylic ester stabilised "homoenolate" anions, from which a series of 4-oxoalkanoic esters (21a ). with a 1,4-D relationship, were prepared (Table 5.6) ... 

In contrast, the so-called bis-nor-Wieland-Miescher ketone (2) is a more complex synthetic problem, since the molecule is a multidissonant system with two dissonant bifunctional group relationships (1,4-D and 1,6-D) and two dissonant cyclopentane rings, besides a 1,5-consonant bifunctional group relationship. Its synthesis was only accomplished 30 years after the synthesis of its consonant homologue [5],... 

Although we have already referred to some rearrangements in connection with the synthesis of dissonant bifunctional relationships, in the present Chapter we will consider those rearrangements which affect mainly the molecular skeleton. 

HP-3 FGI, in order to introduce a C=0 group, modify a double bond or to proceed to a "reactivity inversion" operation Umpolung) in dissonant bifunctional relationships (see below iii-a). 

HP-4 EGA, in order to functionalise or create new consonant bifunctional relationships (new dissonances must be avoided) sometimes, introduce a double bond prior to disconnection of bonds (conjugated if a C=0 group is already present). 

CHAOS, of course, also finds and shows (if required) all the bifunctional relationships which are classified as "consonant" and "dissonant". 

We have considered the effects of attitudes on behaviour, but what of the effects of behaviour on attitudes It may appear surprising to consider the effects of behaviour on attitudes, as it is normally assumed that the relationship is the other way around. There is, however, considerable evidence to show that, under certain circumstances, behaviour can have a considerable influence on attitudes. There are two main theories that explain this effect, those of cognitive dissonance and self-perception theory. For some time it was thought that these theories were in conflict, but recent research has shown that they explain different effects. 

Cognitive dissonance theory The theory of cognitive dissonance, developed by Leon Festinger (1962), has been one of the most influential theories in social psychology. Festinger s fundamental assumption, for which there is considerable evidence, is that people like to see themselves, and be seen by others, as being consistent. This also applies to the relationship between attitudes and behaviour. What interested Festinger, therefore, was the situation in which there was a contradiction between a... 

Evans has refered to even and odd difunctional relationships as dissonant and consonant for reasons that will become apparent. 

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