Caramelisation in food and beverages

One-pot multi-step reactions based on thiolactone chemistry: A powerful synthetic tool in polymer science

Some 25 years have elapsed since the topic of metalation reactions was reviewed by Gilman and Morton. The intervening years have been notable for intensive explorations in this area, in part because many organolithium reagents are now commercially available. Specifically, research efforts have been characterized by the discovery of new functional groups that promote metalation, elaboration of novel heterocyclic and olefinic substrates as metalatable species, recognition of new types of lithiating agents, and the continuation of efforts to define accurately the mechanism of metalation. Accordingly, heteroatom-facilitated lithiation has become recognized as an increasingly important tool, not only in the elaboration of carbocyclic aromatic and heteroaromatic systems, but also in synthetic aliphatic chemistry. A few recent reviews have covered the topic in a more limited or less specific sense. It is the purpose of this chapter to survey and classify the vast accumulation of heteroatom-facilitated lithiations recorded since the first coverage in Organic Reactions.



As outlined by Gilman and Morton, the terms “metalation” in general and “lithiation” in particular denote any replacement of a hydrogen atom by metal or lithium. In this review, however, lithiation is defined as the exchange of a hydrogen atom attached to an sp2-hybridized carbon atom by lithium to form a covalent lithium-carbon bond. More specifically, discussion is limited to those metalations that, through the influence of a heteroatom, are characterized by rate enhancement and regioselectivity. In fact, lithiation reactions of this type are noted for an extraordinarily high degree of regioselectivity, metalation generally occurring on the sp2-carbon atom closest to the heteroatom. Based on the relative position of the heteroatom, such lithiations are conveniently classified into two principal categories: alpha and beta (ortho) lithiations.



In alpha lithiations the metalating agent deprotonates the sp2-carbon atom alpha to the heteroatom to form a carbonlithium bond. This sp2-carbon atom may be part of an olefinic or heteroaromatic π system.



In beta lithiations the metalating agent is directed to deprotonate the sp2-carbon atom beta to the heteroatom-containing substituent. The sp2-carbon atom can be part of an aromatic or an olefinic π system. It should be noted that the designation “ortho metalation” is used specifically for the beta metalation of carbocyclic aromatic systems.



This chapter surveys all systems in which alpha and beta lithiations have been observed, with the exception of ferrocenes.


Keywords:

lithiations;
alpha lithiations;
beta lithiations;
scope;
limitations;
alpha activating atom;
oxygen;
sulfur;
nitrogen;
selenium;
tellurium;
halogens;
beta-directing atom;
substrates;
enamines;
vinyl isocyanides;
formamides;
pyrroles;
indoles;
pyrazoles;
imidazoles;
triazoles;
tetrazoles;
alkyl vinyl ethers;
pyrazoles;
pyridines;
pyrimidines;
furans;
oxazolines;
oxazoles;
sulfides;
sulfoxides;
thiophenes;
electron-withdrawing groups;
vinyl halogens;
amines;
ethers;
sulfones;
amides;
alcohols;
ketones;
experimental procedures

Heteroatom‐Facilitated Lithiations

The current state and prospects of development of the chemistry of isomeric thienopyridines (synthesis, chemical transformations, and biological activities) are analyzed. Particular attention is given to studies published in the last 10–15 years.

Thienopyridines: synthesis, properties, and biological activity

Caramel, defined as coloring agent and as an antioxidant, is being used in several kinds of food products. It has been classified into 4 classes to satisfy the requirement of several food and beverage systems. The variation in its consistency owing to its basic content of milk solids, sugars, and fat has been studied. Several methods have been found to estimate the amount of color provided by caramel in food products. Various formulations have been cited for the production of caramel by eradicating the frequent areas of problems during its processing. Caramel has been used as a synthetic colorant replacer in the baking and beverage industries. Researchers have aimed to ascertain the contribution to the antioxidant activity of some caramel-containing soft drinks. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has established an acceptable daily intake (ADI) of Class I caramel color as “not specified”; that of Class II as 0–160 mg/kg body weight; that of Class III as 0–200 mg/kg body weight; and that of Class IV as 0–200 mg/kg body weight. This paper is an overview of the classification, physicochemical nature, formulations, coloring properties, antioxidant properties, and toxicity of caramel in different food systems.

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Food caramels: a review.

Analysis of aromatic caramel

/pdf/synthesis-of-indolizine-6-9-diones-annelated-to-a-thiophene-40ryxlwhx1.pdf

Synthesis of indolizine-6,9-diones annelated to a thiophene ring

Sur la synthese d'isosteres thiopheniques des flavones, thioflavones et xanthones

Meisenheimer complexes. 1,1 and 1,3 Adducts from 2,6-dinitro-4-trifluoromethylsulfonyl- and 4-methylsulfonylanisoles. Kinetics in methanolic dimethyl sulfoxide

Cyclisations intramoléculaires: Accés aux 9-oxo-4H,9H-pyrrolo[1,2-a]thieno[2,3-d]pyridine et 4-oxo-4H,9H-pyrrolo[1,2-a]thieno[2,3-d]pyridine. Synthèse des pyrrolo[1,2-a]thieno[3,2-e][1,4]diazepine et pyrrolo[1,2-a]thieno[2,3-e][1,4]diazepine

Jean Morel

Papers

Analysis of aromatic caramel

Synthesis of indolizine-6,9-diones annelated to a thiophene ring

Sur la synthese d'isosteres thiopheniques des flavones, thioflavones et xanthones

Meisenheimer complexes. 1,1 and 1,3 Adducts from 2,6-dinitro-4-trifluoromethylsulfonyl- and 4-methylsulfonylanisoles. Kinetics in methanolic dimethyl sulfoxide

Cyclisations intramoléculaires: Accés aux 9-oxo-4H,9H-pyrrolo[1,2-a]thieno[2,3-d]pyridine et 4-oxo-4H,9H-pyrrolo[1,2-a]thieno[2,3-d]pyridine. Synthèse des pyrrolo[1,2-a]thieno[3,2-e][1,4]diazepine et pyrrolo[1,2-a]thieno[2,3-e][1,4]diazepine