Reactivity of conjugated system

This area has received much less attention in the literature than the reactivity of conjugated systems. As noted in CHEC-II(1996) <1996CHEC-II(8)345>, most of the examples studied contain one or two oxo groups in the six-membered ring and are cyclic amide tautomers of the corresponding hydroxyl compounds. 

Our laboratory developed a new synthetic approach to (l-2)-iS-thiodisaccharides (26) utilizing the reactivity of conjugated system of isolevoglucosenone. This synthetic approach (scheme 11) constitutes a general methodology, similar to our previously reported synthesis of (1-4)-iS,-3-deoxythidosacharides (27-28). 

It has been observed that some conjugated polyenes can be selectively hydroborated with borane, 3) (Chart 3) probably due to the low reactivity of conjugated system in the intermediate organoborane. In some cases, the diene moiety within the polyene system has been protected by complexation 14-16). 

The study aids for this chapter include key terms and concepts (which are hyp>erlinked to the Glossary from the hold, hlue terms in the WileyPLUS version of the hook at wileyplus.com) and a Concept Map relating to properties and reactivity of conjugated systems and the Diels-Alder reaction. 

I WORKED EXAMPLES INTEGRATING THE CONCEPTS 14-30. Exploring the Reactivity of Conjugated Systems... 

Conjugare is a Latin verb meaning to link or yoke together and allylic carbocations allylic free radicals and conjugated dienes are all examples of conjugated systems In this chapter we 11 see how conjugation permits two functional units within a molecule to display a kind of reactivity that is qualitatively different from that of either unit alone... 

Allylic carbocations and allylic radicals are conjugated systems involved as reactive intermediates m chemical reactions The third type of conjugated system that we will examine conjugated dienes, consists of stable molecules... 

Since the degree of conjugation in group III and IV metal-containing heterocycles has not been investigated, the reactivity of all systems of interest is discussed in the following section. 

Furthermore, the reactivity of a leaving group X in heterocyclic systems such as 7 (86M1305) and 8 (Section 1V,D) is dramatically increased by conjugation with a carbonyl group. The reactivity of these systems with amines is further enhanced by addition of a proton or Lewis acid to the carbonyl group in 7 or 8 (cf. 150-166). 

Conjugated dienes are deactivated relative to isolated double bonds towards 9-BBN-H, so monohydroboration is difficult to achieve unless the second hydroboration stage is slowed by intrinsic lack of reactivity of the system or by steric crowding, when it is possible to produce allylic organoboranes e.g. equation 33). ... 

Copolymers containing conjugated double bonds are expected to react with halogens more easily and selectively than copolymers containing olefinic double bonds because of the high reactivity of dienic systems. Furthermore, the possibility... 

Reactivity of the 9, 19-Cyclo-l 1-keto Conjugated System The reactivity of this system has been studied in the case of the cycloxobuxines (149) and the cycloxobuxidines (150) ... 

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