High -selectivity

As far as the parallel byproduct reaction is concerned, for high selectivity, if... 

High selective performance of the sensor also enable to detect surface cracks in ferromagnetic and non-magnetic welded connections under rust or dirt layer without prior cleaning. 

Early laser Isotope separation after IR multiphoton excitation high selectivity at room temperature... 

IR-UV double resonance also selective for S and C Reaction of both Isotopes with high selectivity (high fluence)... 

Moreover, multivariate optimization, the simultaneous optimization of several properties, will increasingly come into focus. A drug should have high selectivity in binding to different receptors and minimal toxicity, good solubility and penetration, and so on. A hair color should have a brilliant shine, be absorbed well, not be washed out, not damage the hair, not be toxic, and be stable under sunlight, etc. 

In general, syn aldol products are achievable with high selectivity, anti aldols are more difficult... 

Copper is clearly the most selective metal-ion catalyst. Interestingly, proton catalysis also leads to high selectivities. This is a strong indication that selectivity in this catalysed Diels-Alder reaction does not result from steric interactions. 

Functional group selectivity is often easy to achieve in reduction and condensation reactions since several highly selective reagents for reduction and for protection offunctional groups are available. 

C = C triple bonds are hydrated to yield carbonyl groups in the presence of mercury (II) ions (see pp. 52, 57) or by successive treatment with boranes and H2O2. The first procedure gives preferentially the most highly substituted ketone, the latter the complementary compound with high selectivity (T.W. Gibson, 1969). 

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

The decarbonylation-dehydration of the fatty acid 887 catalyzed by PdCl2(Ph3P)2 fO.Ol mol%) was carried out by heating its mixture with acetic-anhydride at 250 C to afford the terminal alkene 888 with high selectivity and high catalyst turnover number (12 370). The reaction may proceed by the oxidative addition of Pd to the mixed anhydride[755]. 

Hydroxylysine (328) was synthesized by chemoselective reaction of (Z)-4-acet-oxy-2-butenyl methyl carbonate (325) with two different nucleophiles first with At,(9-Boc-protected hydroxylamine (326) under neutral conditions and then with methyl (diphenylmethyleneamino)acetate (327) in the presence of BSA[202]. The primary allylic amine 331 is prepared by the highly selective monoallylation of 4,4 -dimethoxybenzhydrylamine (329). Deprotection of the allylated secondary amine 330 with 80% formic acid affords the primary ally-lamine 331. The reaction was applied to the total synthesis of gabaculine 332(203]. 

The reaction of isoprcnc with Et NH in the presence of triethylammonium iodide (10 mol%) gives the 1 1 adducts 51 and 52 with high selectivity(53]. The reaction of isoprene with ammonia or diethylamine affords the tail-to-tail dimer 53 when Pdfacac) and (BuO)jP are used as the catalyst. The head-to-head dimer 54 is obtained with Pd(acac)2, BF,. and tricyclohexylphosphine(54]. 

Bromine reacts with alkanes by a free radical chain mechanism analogous to that of chlorine There is an important difference between chlorination and brommation how ever Brommation is highly selective for substitution of tertiary hydrogens The spread m reactivity among pnmary secondary and tertiary hydrogens is greater than 10 ... 

Although alkenes typically react with chlorine and bromine by addition at room tern perature and below (Section 6 14) substitution becomes competitive at higher tempera tures especially when the concentration of the halogen is low When substitution does occur It IS highly selective for the allylic position This forms the basis of an industrial preparation of allyl chloride... 

The comparative ease with which a benzylic hydrogen is abstracted leads to high selectivity m free radical halogenations of alkylbenzenes Thus chlorination of toluene... 

Hydrogenation of the side chain double bond of an alkenylbenzene is much easier than hydrogenation of the aromatic ring and can be achieved with high selectivity leav mg the ring unaffected... 

Halogenation (Section 11 12) Free radical halo genation of alkylbenzenes is highly selective for substitution at the benzylic position In the exam pie shown elemental bromine was used Alterna Lively N bromosuccinimide is a convenient re agent for benzylic bromination... 

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