Lithium pyridyls

Demailly and coworkers195 found that the asymmetric induction increased markedly when optically active methyl pyridyl sulfoxide was treated with an aldehyde. They also synthesized (S)-chroman-2-carboxylaldehyde 152, which is the cyclic ring part of a-tocopherol, by aldol-type condensation of the optically active lithium salt of a,/3-unsaturated sulfoxide. Although the diastereomeric ratio of allylic alcohol 151 formed from lithium salt 149 and 150 was not determined, the reaction of 149 with salicylaldehyde gave the diastereomeric alcohol in a ratio of 28 72196. 

Natriumboranat/Pyridin > Lithium-tetrakis-[l,2-dihydro-pyridyl-(l)]-aluminat > Natriumboranat/Alkohol > Lithium-tri.-tert.-butyloxy-hydrido-aluminat > Lithiumalanat > Lithium-trimethoxy-hydrido-aluminat > Aluminiumhydrid > Bis-[2-methyl-propyl]-aluminiumhydrid... 

Pyridyl-l,3-dithianes (50) result from the reaction of picolyl lithium reagents with 1,2-dithiolanes in the presence of HMPT. An initial ring opening is followed by reaction at the carbanion site with a second mole of dithiolane <96PS(112)101>. 

The scope and limitations were briefly studied. Unfortunately the scope of the reaction was rather narrow, as shown in Table 1.4. The Emit of generality may originate from differences in aggregation of each individual lithium acetylide. For instance, changing 2-pyridyl to 3-pyridyl, the ee dropped to 36%. Furthermore, changing to 4-pyridyl, the ee further decreased to 13%. Fortunately, asymmetric addition of a TMS protected acetylide provided the desired adduct in 82% ee. Since... 

Reaction of [Ir(cod)Cl]2 with (6-methyl-2-pyridyl)methyl lithium yields the binuclear species [(cod)Ir(/i-CH2-py-6-Me-C, /V)]2, (401). The Ir centers in (401) are 3.5889(3) A apart, indicating little metal-metal interaction. Treatment of (401) with PPh2Et yields [(cod)Ir(PPh2Et)2(CH2-py-6Me)], which contains the monodentate, carbon-bound pyridylmethyl ligand. 

Since the nitrogen in pyridine is electron attracting it seemed reasonable to predict that the trihalopyridynes would also show the increased electrophilic character necessary to form adducts with aromatic hydrocarbons under similar conditions to those employed with the tetra-halogeno-benzynes. The availability of pentachloropyridine suggested to us and others that the reaction with w-butyl-lithium should lead to the formation of tetrachloro-4-pyridyl-lithium 82 84>. This has been achieved and adducts obtained, although this system is complicated by the ease with which pentachloropyridine undergoes nucleophilic substitution by tetrachloro-4-pyridyl lithium. Adducts of the type (45) have been isolated in modest yield both in the trichloro- and tribromo- 58) series. 

An attempted synthesis, Scheme 65, of a heterozincate from dimethylzinc and bis (2-pyridyl)methyl lithium gave instead the dimeric [bis (2-pyridyl)methyl methylzinc] complex 84, shown in Figure 43.143 The intermolecular zinc-carbon bond to the bridging carbon atoms is remarkably short (2.269(3) A), while the zinc-methyl bond is slightly elongated (1.974(3) A). 

Preparation.—From Halogenophosphine and Organometallic Reagents. The cyclo-pentadienylphosphines (1) have been obtained from the reaction of cyclopenta-dienylthallium with chlorophosphines in ether.1 Diphenyl(4-pyridyl)phosphine (2) is prepared from 4-pyridyl-lithium and chlorodiphenylphosphine,2 and an improved procedure for the synthesis of tri-(2-pyridyl)phosphine (3) from 2-pyridyl-lithium and phosphorus trichloride has been reported.3... 

Phosphorus ylides have been reviewed and an intermediate betaine lithium salt adduct (stabilized by complexation with lithium ions and by the chelating effect of pyridyl ligands) has been observed spectroscopically for the first time during the course of a Wittig reaction. ... 

A number of groups have been found to direct and stabilize o-metallation in aromatic systems since Meyers ( ) introduced the oxazolidine group for this purpose. It was reasoned that the imidazolinone group should also serve this purpose. It was gratifying to find that treatment of the pyridyl imidazolinone 22 th 2.2 equivalents of butyl lithium followed by carbon dioxide gave a good yield of the nicotinic acid 14 (R=H). 

The (—)-sparteine-complex of l-(2-pyridyl)-l-(trimethylsilyl)methyllithium is monomeric and shows, according to an X-ray analysis, an almost planar methine group. The lithium cation is placed in a -fashion above the plane of the azaallyl anion moiety. 

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