Compatibility functional groups, reactivity

Alkenes can add to double bonds in a reaction different from those discussed in 15-19, which, however, is still formally the addition of RH to a double bond. This is called the ene reaction or the ene synthesis For the reaction to proceed without a catalyst, one of the components must be a reactive dienophile (see 15-58 for a definition of this word) such as maleic anhydride, but the other (which supplies the hydrogen) may be a simple alkene such as propene. Cyclopropene has also been used. ° The reaction is compatible with a variety of functional groups that can be appended to the ene and dienophile. N,N-Diallyl amides give an ene cyclization. 

As an example of the selective reactivity of borazirconocene alkenes, their hydrolysis was examined [1]. The carbon—zirconium bond is more reactive than the carbon—boron bond towards various electrophiles, and so hydrolysis can be expected to occur with preferential cleavage of the former bond. Since hydrolysis of alkenylzirconocenes is known to proceed with retention of configuration [4,127—129], a direct utility of 45 is the preparation of (Z)-1-alkenylboronates 57 (Scheme 7.17) [12]. Though the gem-dimetalloalkenes can be isolated, in the present case it is not necessary. The desired (Z)-l-alkenylboronates can be obtained in a one-pot procedure by hydrozirconation followed by hydrolysis with excess H20. The reaction sequence is operationally simple and is compatible with various functional groups such as halides, acetals, silanes, and silyloxy protecting groups [12]. 

These protocols were applied to pyridines, quinolines, and naphthyridines. They are compatible with other functional groups, for instance, acid derivatives. Dehydration can be effected by a chemical process (chlorinating agents), or simply by heating. Method A3 generally required harsh conditions, since in most examples no base was added for HC1 consumption, therefore lowering the reactivity of the pyridine nitrogen, present as its hydrochloride salt. 

In order to prepare successful NIR molecular probe dyes, NIR dyes must meet the following criteria adequate response to analytes, high lipophilicity and/or reactive functional groups, absorbance maxima compatible with available laser diodes, high fluorescence quantum yield, molar absorptivity, and high photostability. 

Several catalytic processes are known, see below, but it is clear that the compatibility of the above chemistry with functionalisation is limited. Many reagents used to introduce functional groups will react with the reactive intermediates described above, and the alkanes will have no opportunity to react with the catalyst. Below a few catalytic reactions will be described of relatively electron-rich metal complexes. 

Most immobilizahon chemistries for microarrays currently rely upon derivatization of the substrate with amine-reactive functional groups such as aldehydes, epoxides, or NHS esters. While we can choose from many available surface-reactive chemistries, it is important to keep in mind that they must be compatible with a printing process. Ideally, the biomolecule should react completely and rapidly with the substrate in order to achieve good spot formation. It is also critical that the probe remain or be recoverable in its active state following printing. If too reactive a chemistry is employed there is the possibility for excessive crosslinking that can hinder performance by reducing the number of rotatable bonds in the probe. 

Conversely, other processes are totally original. This is especially encountered when the electrochemical act is associated with a transition metal complex catalysis. These methods have the advantage of affording the organozinc compound synthesis under simple and mild conditions that are compatible with the presence of reactive functional groups on the substrate. Importantly, these procedures are reproducible and can be run by any chemist. Besides, the preparation from a few millimoles to tens of millimoles of the organometallic compound is easy at the laboratory scale. 

Glycopeptides contain many functional groups of different reactivity as well as O- and /V-glycosidic bonds. Therefore, the compatibility and chemoselectivity of the applied reactions is a fundamental prerequisite in glycopeptide synthesis. In this chapter, efficient and generally applicable methods and their combinations will be illustrated by examples [5,8,91. 

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