Derivatives, formation general discussion

The aim of this article is to review the different systems where such reactions have been observed, to discuss some of the proposed mechanisms for oligomer formation and finally to try to derive some general rules which govern this kind of reactions. 

The discussion of this somewhat heterogeneous collection of free and substituted dicarbonyl carbohydrates will be divided into (a) dialdehyde compounds, (b) keto-aldehyde compoimds having free or substituted carbonyl groups, and (c) the diketo compounds. Each Section (except the last one, containing only a few members) will be divided into (a) an introduction consisting of a general discussion concerning formation and preparation, (b) a description of individual compounds, and (c) a discussion of properties and reactions. A short discussion on oxidized polysaccharides is included before the Tables of dicarbonyl carbohydrates and their derivatives. 

Finally, the C—C bond formation by the reaction of 7r-complexes of Pd derived from alkenes, dienes, and other 7r-compounds with enolates and related carbon nucleophiles a la Wacker reaction (Method VI in Scheme 1) provides yet another alternative, as exemplified by the results shown in Scheme For a more general discussion of the C—C bond formation via Wacker-type reaction of Pd rr-complexes with carbanions, the reader is referred to Sect. V.3.4. 

Many versatile approaches to the construction of fused heterocyclic systems (6 5 6) with ring junction heteroatoms have been reported. More general reactions which can be used for synthesis of derivatives of several tricyclic systems, and transformations which have potential for use in the preparation of a series of substituted compounds, are discussed in this section. Formation of the five-membered ring is presented first because it is a conceptually simple approach. It should be noted, however, that the addition of a fused six-membered ring to a bicyclic component offers much more versatility in the construction of a (6 5 6) system. Each subsection below starts with intramolecular cyclization of an isolated intermediate product. Reactions which follow are one-pot intermolecular cyclizations. 

The reaction of ADC compounds with carbenes and their precursors has already been discussed in Section IV,A- In general, the heterocyclic products are not the result of 1,2-addition but of 1,4-addition of the carbene to the —N=N—C=0 system.1 Thus the ADC compound reacts as a 4n unit in a cheletropic reaction leading to the formation of 1,3,4-oxadiazolines. Recent applications include the preparation of spiro-1,3,4-oxadiazolines from cyclic diazoketones and DEAZD as shown in Eq. (14),133 and the synthesis of the acyl derivatives 85 from the pyridinium salts 86.134 The acyl derivatives 85 are readily converted into a-hydroxyketones by a sequence of hydrolysis and reduction reactions. 

When starting this chapter we promised ourselves and the reader not to consider benzene and its derivatives. Cyclooctatetraene [or more properly (Z,Z,Z,Z)-l,3,5,7-cyclooctatetra-ene, 147] is generally recognized as a polyene and so this latter compound would appear to belong here. How can we do one and not the other Therefore, in this concluding section of the chapter, we briefly discuss the enthalpies of formation of some of the... 

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