Deprotonation Subject

Like mthenium, amines coordinated to osmium in higher oxidation states such as Os(IV) ate readily deprotonated, as in [Os(en) (NHCH2CH2NH2)] [111614-75-6], This complex is subject to oxidative dehydrogenation to form an imine complex (105). An unusual Os(IV) hydride, [OsH2(en)2] [57345-94-5] has been isolated and characterized. The complexes of aromatic heterocycHc amines such as pyridine, bipytidine, phenanthroline, and terpyridine ate similar to those of mthenium. Examples include [Os(bipy )3 [23648-06-8], [Os(bipy)2acac] [47691-08-7],... 

Examine and eompare eleetrostatie potential maps for the eycloalkanes. Is there any evidenee of earbon-carbon bonds being espeeially eleetron rieh (subject to electrophilic attack), or of CH bonds being espeeially electron poor (subject to deprotonation) ... 

In the reaction of amines such as NH3, NH2NH2, MeNH2, C6HUCH2NH2, and Ph(OMe)NH2, only monosubstitution can be obtained even in the presence of a large excess of the amine. This is taken into account by the deprotonation of the acidic monosubstituted complex by free amine leading to an iminocyclohexadienyl complex. The latter cannot be subjected to nucleophilic substitution of the second... 

The starting benzothiazole carboxylic ester 387 was subjected to a Anamination by using mesityl hydroxylamine to give an A -amino salt 388, which was treated with a tertiary amine to give the deprotonated intermediate 389. This species when reacted with phenylisocyanate yielded the final product 390 in moderate yield <2001JOC8528>. 

Novel alkenylphosphonium salts were subjected to the Wittig reaction (Scheme 12). Allylic deprotonation took place for phosphonium salts possessing such protons, and the olefination proceeded after double bond migration. In cases where such protons were absent, allene formation was observed. 

It is obvious that the isobutene unit provides a good starting point for the generation of trimethylenemethane radical anions. However, even isobutane units can be used to produce these more highly unsaturated species. In a preliminary work aimed at two-and three-fold deprotonation processes in solution, Kuck, de Meijere and coworkers165 have subjected triquinacene (41) and the tribenzotriquinacenes 44 to NCI conditions with... 

Enders and co-workers based their synthesis of (.R)-(-)-phoracantholide I (245) on their well-known SAMP methodology (Scheme 13) [205]. Thus, the SAMP derivative of cyclononanone (252) was deprotonated with LDA at 0 °C, and the resulting enolate was treated with CH3I at -100 °C to afford the a-methylated product 253 with >93% de. The latter was ozonized at -78 °C, and the resulting ketone (254) subjected to a Bayer-Villiger reaction to afford ( )-(-)-245 with 91% ee. 

The y-lactone degradation products of cefdinir were found to be also subject to C(6)-epimerization in neutral to basic solutions. The mechanism proposed for this epimerization involves deprotonation of the enamine N-atom,... 

The broader subject of the interaction of stable carbenes with main-group compounds has recently been reviewed. Accordingly, the following discussion focuses on metallic elements of the s and p blocks. Dimeric NHC-alkali adducts have been characterized for lithium, sodium, and potassium. For imidazolin-2-ylidenes, alkoxy-bridged lithium dimer 20 and a lithium-cyclopentadienyl derivative 21 have been reported. For tetrahydropyrimid-2-ylidenes, amido-bridged dimers 22 have been characterized for lithium, sodium, and potassium. Since one of the synthetic approaches to stable NHCs involves the deprotonation of imidazolium cations with alkali metal bases, the interactions of alkali metal cations with NHCs are considered to be important for understanding the solution behavior of NHCs. 

Electron-rich olefins are nucleophilic and therefore subject to thermal cleavage by various electrophilic transition metal complexes. As the formation of tetraaminoethylenes, i.e., enetetramines, is possible by different methods, various precursors to imidazolidin-2-ylidene complexes are readily available. " Dimerization of nonstable NHCs such as imidazolidin-2-ylidenes is one of the routes used to obtain these electron-rich olefins [Eq. (29)]. The existence of an equilibrium between free NHC monomers and the olefinic dimer was proven only recently for benzimidazolin-2-ylidenes. In addition to the previously mentioned methods it is possible to deprotonate imidazolidinium salts with Grignard reagents in order to prepare tetraaminoethylenes. " The isolation of stable imidazolidin-2-ylidenes was achieved by deprotonation of the imidazolidinium salt with potassium hydride in THF. ... 

The Z-alkene ( ) was subjected to the same sequence (Scheme 4). The triflate ( ) was easily obtained, but in this case reaction with azide ion gave directly the diazoester (22). Molecular models show that the triazoline corresponding to (19) has severe steric interactions and is more accessible to deprotonation (cf. ref. 23). 

When the tertiary center in 6 containing the chiral auxiliary is subjected to deprotonation/ benzylation the stereoselective formation of l-benzyl-l,2,3,4-tetrahydro-l-methylisoquinoline (97-98% ee) was reported which interestingly had the R configuration. Hence, the monoalky-lated intermediate related to 8 is alkylated from the bottom face, opposite to that found with unsubstituted 5. Obviously the existence of two diastereomeric lithiocompounds accounts for these results. Now the strong temperature dependence of the selectivity, which usually hints that an equilibrium is involved, can also be easily understood. 

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