Introduction of functional

Polymer Modification. The introduction of functional groups on polysdanes using the alkah metal coupling of dichlorosilanes is extremely difficult to achieve. Some polymers and copolymers with 2-(3-cyclohexenyl)ethyl substituents on siUcon have been made, and these undergo hydrogen hahde addition to the carbon—carbon double bond (94,98). 

In general bromination of 20-ketones is directed to the introduction of functionality at C-21. However, on occasion 17-bromo compounds are required for dehydrobromination to A -20-ketones, although these are generally obtained in other ways. Kinetic enolization of a 20-ketone gives the A °-enol, whereas the thermodynamic product is the A kjsomer. An interesting enolate trapping reaction has been used recently to prepare 16-methyl-A -20-ketones ... 

Multistage emulsion polymerization techniques are usually applied for (1) the synthesis of large uniform latex particles, (2) the introduction of functional groups into the uniform latex particles, or (3) the synthesis of macroporous uniform latex particles. 

The pharmaceutical interest in the tricyclic structure of dibenz[6,/]oxepins with various side chains in position 10(11) stimulated a search for a convenient method for the introduction of functional groups into this position. It has been shown that nucleophilic attack at the carbonyl group in the 10-position of the dibenzoxepin structure renders the system susceptible to water elimination. Formally, the hydroxy group in the enol form is replaced by nucleophiles such as amines or thiols. The Lewis acids boron trifluoride-diethyl ether complex and titanium(IV) chloride have been used as catalysts. 

Scheme 14. Introduction of functionality in secondary P-chirogenic phosphines...

ELPs can be produced via chemical synthesis and biosynthetically. For chemical synthesis via solid phase peptide synthesis, the attainable polymer length is limited, and if long polymers with a defined length are required then the biosynthetic approach is more appropriate. An advantage of chemical synthesis is, however, that it enables the facile introduction of functional residues in the polypeptide [27]. 

Introduction of Functional Groups by Nucleophilic Substitution at Saturated Carbon... 

In this section we focus on intramolecular functionalization. Such reactions normally achieve selectivity on the basis of proximity of the reacting centers. In acyclic molecules, intramolecular functionalization normally involves hydrogen atom abstraction via a six-membered cyclic TS. The net result is introduction of functionality at the S-atom in relation to the radical site. 

Initial efforts gave rise to well-characterized dendritic macromolecules, but applications remained limited because of the lack of specific functionalities. An exponential increase of publication volume observed for about 15 years testified the growing interest for dendrimers and has led to versatile and powerful iterative methodologies for systematically and expeditiously accessing complex dendritic structures. The perfect control of tridimensional parameters (size, shape, geometry) and the covalent introduction of functionalities in the core, the branches, or the high number extremities, or by physical encapsulation in the microenvironment created by cavities confer such desired properties as solubility, and hydrophilic/hydrophobic balance. Thus, creativity has allowed these structures to become integrated with nearly all contemporary scientific disciplines. 

Inman, J.K., and Dintzis, H.M. (1969) The derivatization of cross-linked polyacrylamide beads. Controlled introduction of functional groups for the preparation of special-purpose, biochemical adsorbents. Biochemistry 8, 4074-4082. 

Bicyclic-monocyclic ion-complex tautomerism The introduction of functional groups onto the substituent at carbon, nitrogen, or phosphorus atoms increases the number of possible types of ion-complex tautomerism. For example, the presence of one more hydroxyalkyl group at the phosphorus atom results in bicyclic-monocyclic tautomerism [Eq. (91)] (85IZV469, 85IZV1102 89IZV946). 

On the whole, the introduction of alkyl substituents at the a-carbon atom leads to a sharp decrease in the rate of [3 + 2]-cycloaddition, that is, nitronates derived from primary AN react much faster than nitronates derived from analogous secondary AN. The introduction of functional EWG groups leads to a substantial increase in the rate of [3 + 2]-cycloaddition. It can also be noted that... 

Some transition metal catalysts induce the living polymerization of various acetylenic compounds.68,69 Such polymerizations of phenylacetylene catalyzed by rhodium complexes are used in conjunction with a quantitative initiation and introduction of functional groups at the initiating chain end (Scheme 16).70 The catalyst is prepared from an [RhCl(nbd)]2/Ph2C=C(Ph)Li/PPh3 mixture and proceeds smoothly to give quantitatively the polymer 54 with a low polydispersity ratio. 

The carbonyl group in a ketone or aldehyde is an extremely versatile vehicle for the introduction of functionality. Reaction can occur at the carbonyl carbon atom using the carbonyl group as an electrophile or through enolate formation upon removal of an acidic proton at the adjacent carbon atom. Although the carbonyl group is an integral part of the nucleophile, a carbonyl compound can also be considered as an enophile when involved in an asymmetric carbonyl-ene reaction or dienophile in an asymmetric hetero Diels-Alder reaction. These two types of reaction are discussed in the next three chapters. 

The ease of converting a nitro group to a carbonyl or other functional group has significantly increased the synthetic potential of nitroalkane derivatives as reagents for the nucleophilic introduction of functionalized alkyl groups in the synthesis of natural products. 

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