Reaction sequences involving combination

In 2007, Wiles et al. (2007c) demonstrated the ability to employ solid-supported catalysts in series within an EOF-based microreactor. As summarized in Scheme 39, the model reaction sequence involved combining a previously investigated acid-catalyzed deprotection with a base-catalyzed condensation reaction to enable the synthesis of a,(3-unsaturated carbonyl compounds from dimethyl acetals. 

The imidazo-benzazepine 43 was prepared in moderate yield by a combination reaction sequence involving an initial van Leusen reaction to prepare the imidazole 42 followed by a microwave-promoted intramolecular Heck reaction <06TL3225>. 

One of the pitfalls of microbial sensors, viz. their low selectivity, can be overcome by combining cells with an immobilized enzyme. Thus, creatinine deaminase (CDA, EC 3.5.4.21) hydrolyses creatinine to N-methylhydantoin and ammonium ion, the ammonia produced being successively oxidized to nitrite and nitrate ion by nitrifying bacteria. These bacteria have not yet been characterized but are known to be a mixed culture of Nitrosomonas sp. and Nitrobacter sp. The reaction sequence involved is as follows ... 

In the following sections of this chapter we will present a few of the kinds of reactions that organic compounds undergo. A topic of such vast scope as reactivity of organic compounds can be made manageable only if we divide our study of this field into subtopics. Nearly all organic transformations involve at least one of three fundamental classes of reactions. The following three sections will address substitution, addition, and elimination reactions. We will also look at some reaction sequences that combine reaction steps from more than one of the fundamental classes. 

The first point that must be established in an experimental study is that one is indeed dealing with a series combination of reactions instead of with some other complex reaction scheme. One technique that is particularly useful in efforts of this type is the introduction of a species that is thought to be a stable intermediate in the reaction sequence. Subsequent changes in the dynamic behavior of the reaction system (or lack thereof) can provide useful information about the character of the reactions involved. 

Reductive sequences involving flavoproteins may be represented as the reverse reaction, where hydride is transferred from the coenzyme, and a proton is obtained from the medium. The reaction mechanism shown here is in many ways similar to that in NAD+ oxidations, i.e. a combination of hydride and a proton (see Box 11.2) it is less easy to explain adequately why it occurs, and we do not consider any detailed explanation advantageous to our studies. We should register only that the reaction involves the N=C-C=N function that spans both rings of the pteridine system. 

Although isoniazid has been in use for about 45 years, the enzyme that it inhibits has been recognized only recently. It is a specific NADH-depen-dent enoyl reductase involved in synthesis of mycolic acids.h/1 The isoniazid must be activated by action of a bacterial catalase-peroxidaseh This enzyme may convert the drug to a reactive radical that combines with a NADH-derived radical to form an adduct in the active site of the enzymes. One possible reaction sequence follows.11 However, the mechanisms are not clear. 

The reaction sequence of Scheme 3 might well be classified as an imidazole synthesis from other heterocycles, but it seems more logical to treat this as a cyclization involving formation of the 1,5-bond. The enaminoketone condensation products (12) of 3-amino-l,2,4-oxadiazoles and 1,3-dicarbonyl compounds are cyclized by base to imidazoles (13) in 60-80% yields." Such a reaction makes use of the well-established general attack of a nucleophilic center in the side chain on N-2 of the oxadiazole ring. Benzamidine combines with 2-amino-3-phenacyl-l,3,4-oxadiazolium bromides to produce 1-acyl-amino-2-benzimidoylamino-4-arylimidazoles. ... 

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