Nonfunctionalized

Asymmetric catalytic epoxidation of nonfunctionalized olefins 93MI3, 98MI1. 

Chemical composition of packings. Today, a wider variety of different support materials is available from which to choose. Silica is still widely used, though preparative grades often possess a relatively wide particle size distribution as compared to polymer-based supports. One serious limitation of silica-based supports is the low stability of silicas to alkaline pH conditions, which limits use of caustic solutions in sanitization and depyrogenation. Polymer-based supports, which include poly(styrene-divi-nyl benzene)- or methacrylate-based materials, are widely available and have gained increased acceptance and use. Nonfunctionalized poly(styrene-divinyl... 

Formal hydration of the double bond appeared by the hydroboration-oxidation sequence. Desymmetrization reactions with catalytic asymmetric hydroboration are not restricted to norbornene or nonfunctionalized substrates and can be successfully applied to meso bicyclic hydrazines. In the case of 157, hydroxy derivative 158 is formed with only moderate enantioselectivity both using Rh or Ir precatalysts. Interestingly, a reversal of enantioselectivity is observed for the catalytic desymmetrization reaction by exchanging these two transition metals. Rh-catalyzed hydroboration involves a metal-H insertion, and a boryl migration is involved when using an Ir precatalyst (Equation 17) <2002JA12098, 2002JOC3522>. 

Just as Wilkinson s catalyst gave rise to the bisphosphine ligands, Crabtree s catalyst [304] spawned the family of phosphorus-nitrogen ligands for simple al-kenes. Subsequently, Pfaltz developed the Phox family, which provides high ee-values with nonfunctionalized alkenes [305-310]. Other analogues are also illustrated in Figure 23.5. 

To be fair, it should be realized that if a catalyst must be recycled for economic reasons, the recycling efficiency compared to the nonfunctionalized catalyst must be higher in order to compensate for the increased price of the fluorous catalyst itself. However, every recycling technique has its own cost that must be evaluated for each specific case. 

The requirement for the presence of an adjacent alcohol group can be regarded as quite a severe limitation to the substrate range undergoing asymmetric epoxidation using the Katsuki-Sharpless method. To overcome this limitation new chiral metal complexes have been discovered which catalyse the epoxidation of nonfunctionalized alkenes. The work of Katsuki and Jacobsen in this area has been extremely important. Their development of chiral manganese (Ill)-salen complexes for asymmetric epoxidation of unfunctionalized olefins has been reviewed1881. 

The epoxidation of nonfunctionalized alkenes may also be effected by chiral dioxiranes. These species, formed in situ using the appropriate ketone and potassium caroate (Oxone), can be formed from C-2 symmetric chiral ketones (29)[93], functionalized carbohydrates (30)[94] or alkaloid derivatives (31)[95]. One example from the laboratories of Shi and co-workers is given in Scheme 19. 

Female gametes of marine brown algae release and/or attract their conspecific males by chemical signals. The majority of these compounds are unsaturated, nonfunctionalized acyclic, and/or alicyclic Cn hydrocarbons. Threshold concentrations for release and attraction are generally... 

It was discussed earlier how a major hurdle for the manipulation of CNTs is their insolubility in most organic and aqueous solvents, and how introducing functional groups is a simple and powerful tool to improve solubility. However, the first functionalization step is expected to be the most problematic due to the primary utilization of as yet nonfunctionalized pristine nanotubes. 

Considering all these features and limitations, it is understandable that currently there is no general procedure available, such as the Fmoc or Boc protocols that are available for nonfunctionalized peptides. However, several approaches have been developed in the last two decades to make lipidated peptides accessible. This chapter describes both the corresponding solution-phase approaches and solid-support approaches for the synthesis of lipidated peptides. In line with the framework sketched above, both the different protecting groups and solid-phase linker systems that have been developed will be reviewed. 

The free radical polymerization of HPMA in the presence of mercaptans involves two different initiation mechanisms (Scheme 2) [26]. One is the initiation by RS radicals from chain transfer agent the other appears to be the direct initiation by the primary isobutyronitrile (IBN) radicals formed by the decomposition of AIBN [27]. The RS are formed by either the free radical transfer reaction of alkyl mercaptans with the IBN radicals or the chain transfer reaction of an active polymer chain with the mercaptans. The initiation by the RS radicals produces the ST polymers with a functional group at one end of the polymer chain. The initiation by IBN radicals leads to nonfunctional polymer chains with an IBN end group. The presence of the polymers with IBN end groups effects the purity and the functionality of ST polymers. As expected, the production of nonfunctionalized polymer chains is affected by reaction conditions. The polymerization is mainly terminated by chain transfer reaction with the mercaptans, but other termination mechanisms, such as disproportionation and recombination, take place depending on the reaction conditions [26]. 

Table I shows the molecular weight and the degree of end group substitution of the monofunctional polystyrene samples obtained. In Table II the corresponding data for the bifunctional samples are given. The samples were characterized by GPC in THF. and were calculated. Comparison with the corresponding nonfunctionalized control samples show good agreement. The results of the light scattering and osmotic pressure experiments with the acid form of the sulfonated polystyrenes were in agreement. No association was observed for THF solutions.

Mononuclear oxazolines are among the most effective ligands for enantioselective hydrogenation of nonfunctionalized alkenes." " The styrene substrate 597 is one of the most studied nonfunctionahzed alkenes used to evaluate the efficiency of new chiral ligands (Scheme 8.185). Selected examples of enatioselective hydrogenation of 597 using iridium catalysts are shown in Table g jg 359,425,426,457-459... 

Amino-3-acylaminopyrimidin-4-ones can be cyclized by base (68ZC142 72ZC20), and nonfunctionalized TP are prepared from 2,3-diaminopyrimidinium salts and C,-synthons (75JHC107). 

To address performance, the results of nonfunctionality tests are considered sufficient if the test and acceptance criteria are appropriate for the intended purpose. Tests described there are typically considered sufficient standards for establishing specified properties and characteristics of specified materials of construction or packaging components. For nonfunctionality tests, an applicant should provide justification for the use of the test, a complete and detailed description of how the test was performed, and an explanation of what the test is intended to establish. If a related test is available, comparative data should be provided using both methods. Supporting data should include a demonstration of the suitability of the test for its intended use and its validation. 

Asymmetric Epoxidation. Asymmetric epoxidation of nonfunctionalized alkenes manifests a great synthetic challenge. The most successful method of asymmetric epoxidation, developed by Katsuki and Sharpless,332 employs a Ti(IV) alkoxide [usually Ti(OisoPr)4], an optically active dialkyl tartrate, and tert-BuOOH. This procedure, however, was designed to convert allylic alcohols to epoxy alcohols, and the hydroxyl group plays a decisive role in attaining high degree of enantiofa-cial selectivity.333,334 Without such function, the asymmetric epoxidation of simple olefins has been only moderately successful 335... 

The synthesis of amino acids in which a nonfunctionalized alkyl group is covalently connected to the a-nitrogen has been discussed vide supra). In this section the synthesis of N-substituted amino acids in which the alkyl chain bears a protected functional group is discussed. The resulting amino acids have the general formula /Va-(m-functionalized alkyl) amino acids 28 (Scheme 17). These amino acids were developed for the solid-phase synthesis of backbone cyclic peptides 70 (see also Vol. E 22b, Section 6.8.3.2.4) [in this case they were called building units (BU)], for the synthesis of PNA 71 and for the synthesis of peptoids. 72 (In this case they were called monomers.)... 

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