Lead lithium amides

Unless a proton donor is added, the lithium-ammonia reduction of an cnone leads to the lithium enolate and lithium amide. The latter is a sufficiently strong base to rapidly convert the mono-alkylated ketone into its enolate, which can be further alkylated. The function of the... 

Diboratacarbazole heterocycles 137 are obtained in 60% isolated yield by heating the phosphine-stabilized 2,2 -diborabiphenyl derivative 138 with primary amines in toluene for 20h (Scheme 55). Further double deprotonation of the heterocycle 137 (Ar = Ph) with a lithium amide leads to the dianionic 9,11-diboratacarbazole derivative 139 (98%, S nB 31.71 ppm). Structures 137 (Ar = Ph) and 139 were characterized by X-ray crystallography <20040M3085>. 

The catalytic system has been successfully extended to polymer-bound lithium amide co-bases of type 65 (see Table 4) which, like C—Li bases of type 63 and 64, are efficient regenerating agents of HCLA and poorly reactive toward oxiranes. For instance, the isomerization of cyclohexene oxide by 0.05 equiv of HCLA 55 in the presence of 1.45 equiv of 65 affords ( l-cyclohexenol in 92% ee (entry 15). It is of interest to note that, similarly to co-bases 63 and 64, the use of 65 leads to an increase of selectivity compared to the stoichiometric reaction at room temperature (Table 2, entry. ... 

Reaction of the chiral lithium enolate of meso-2,6-dimethylcyclohexanone (6), generated by deprotonation with (R)-l-phenylethylamine and (/ )-camphor/(R)-l-phenylethylaniine derived chiral lithium amides (Table 1, entries 17 and 64) with 3-bromopropene, leads to homoallyl ketones of opposite absolute configuration in acceptable yield with poor to modest enantiomeric excess14, which can be determined directly by H-NMR spectroscopy in the presence of tris [3-(heptafluorohydroxymethylene)-D-camphorato]europium(III) [Eu(hfc)3]. 

Deprotonation of tropinone (1) with various chiral lithium amides and external quenching of the lithium enolate with benzaldehyde gives the aldol product 2 in moderate to good yield with moderate enantiomeric excess but high diastcrcosclcctivity. The aldol product 2 is a single diastereomer with the relative configuration as depicted, but of unknown absolute configuration19. Recrystallization of the aldol product leads to enantiomerically pure material. 

Table XIII (189-199) gives details of solid-state lithium amide monomeric complexes (69)—(87). These include just three [(79), (80), and (87)] solvent-separated ion pairs. The remainder are contact-ion pairs, each with an (amido)N—Li bond. Association to dimers or higher oligomers is prevented sterically. The size of the R and/or R group in the RR N- anions can lead to monomers even when Li+ is complexed only by a single bidentate (e.g., TMEDA) or by two monodentate (e.g., THF or Et20) ligands. In such cases [(69), (71), (72), (75)-(78), and (81)—(83) ], the lithium centers are only three coordinate. Electronic factors in the anion [notably, B N multiple bonding in (75)—(78) ] also may reduce the charge density at N, and lower the ability to bridge two...

Lanthanum nitrate, analysis of anhydrous, 5 41 Lead (IV) acetate, 1 47 Lead(II) 0,0 -diethyl dithiophos-phate, 6 142 Lead (IV) oxide, 1 45 Lead(II) thiocyanate, 1 85 Lithium amide, 2 135 Lithium carbonate, formation of, from lithium hydroperoxide 1-hydrate, 5 3 purification of, 1 1 Lithium chloride, anhydrous, 6 154 Lithium hydroperoxide 1-hydrate, 5 1... 

Reaction between 3-amino-2-thiophenecarboxylic acid and R2GeCl2 with a deficiency of the L1NH2 gives the monoamino compounds 158 while an excess of lithium amide leads to formation of the diamino derivatives 159513 515-516 p(le authors suggest that intermolecular O — Ge coordination increases the lability of chlorine substituent in the intermediate 158 and favors the formation of the diamino derivatives 159510 513-515... 

There is only one exception to the last statement in that aldehydes cannot be converted quantitatively into aldehyde enolates. Any attempt to achieve a quantitative deprotonation of an aldehyde—with a lithium amide, for example—necessarily leads to a situation in which some aldehyde enolate is formed while some aldehyde substrate is still present, and these species cannot coexist even at temperatures as low as that of dry ice. The aldehyde is such an excellent electrophile that it reacts much faster with the enolate than it is deprotonated by the base. 

Desymmetrisation of the enantiotopic methyl groups of 432 with a chiral lithium amide base leads to atropisomeric amides in good enantiomeric excess.186... 

Desymmetrisation by enantioselective ortholithiation has been achieved with ferrocenylcarboxamides 434,187 and also (with chiral lithium amide bases) a number of chromium-arene complexes.188 The chromium arene complex 435, on treatment with s-BuLi-(-)-sparteine, gives 436 enantioselectively, and reaction with electrophiles leads to 437. However, further treatment with r-BuLi generates the doubly lithiated species 438, in which the new organolithium centre is more reactive than the old, which still carries the (-)-sparteine ligand. Reaction of 438 with an electrophile followed by protonation therefore gives ent-431.m... 

The authors favor the nucleophilic addition of lithium amide to arylthiodifluoroolefin 7 leading to a-fluoroenamine 8 and finally to 9 (Path A). Nevertheless, intermediacy of 9 cannot be entirely discarded (Path B). 

The observation by Fischer et al.18 that the 4,1-addition of dimethylamine to compound la is thermodynamically controlled at 20°C, whereas 2,1-addition/elimination is kinetically controlled at -115°C, turned out to be limited to few cases.20 It has been shown9a 9b 42 112 113 that for most cases, three competing reaction paths must be considered (i) 2,1-addition/elimina-tion with formation of (l-amino)alkynylcarbene complexes (= 2-amino-l-metalla-l-en-3-ynes) 98 (ii) 4,1-addition to give [(2-amino)alkenyl]carbene complexes (= 4-amino-l-metalla-l,3-butadienes) 96 and (iii) 4,1-addition/ elimination to (3-amino)allenylidene complexes (= 4-amino-l-metalla-1,2,3-butatrienes) 99 (Scheme 33, M = Cr, W). The product ratio 96 98 99 depends on the bulk of substituents R and R1, as well as on the reaction conditions. Addition of lithium amides instead of amines leads to predominant formation of allenylidene complexes 99.112 Furthermore, compounds 99 also can be generated by elimination of ethanol from complexes 96 with BF3 or AlEt3114 and A1C13,113 respectively. 

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