Lithium, butyl-, reaction with cyclic

It was observed that ammonolysis of B(C2H,Si(R)H2)3 (Scheme 2, route A) requires basic catalysts such as n-butyl lithium. The reaction is performed in analogy to the potassium hydride-catalyzed cross-linking of cyclic silazanes described by Seyferth et al. [8]. Most probably, n-BuLi initially deprotonates the weak nucleophile ammonia with the formation of lithiiun amide and evaporation of n-butane. The stronger nucleophilic amide then replaces a silicon-bonded hydride, which subsequently deprotonates ammonia, leading to the evolution of molecular hydrogen. The silylamines that arise are not stable under the reaction conditions applied (refluxing solvent), and by fast condensation of ammonia the polymeric precursors form [6]. 

The presence of a heterosubstituent facilitates deprotonation. For example, the metalation of cyclic vinyl ethers with n-butyl-lithium/potassium tert-butoxide bas been successfully employed in the synthesis of C-glycosides. This reaction proceeds via metalation of the glucal, followed by reaction with tributyltin chloride, to afford the corresponding tin derivative that can be submitted to transition metal-catalyzed cross-coupling reactions (eq 9). 

The reaction is believed to proceed via a six-membered cyclic transition state, analogously to the carbonyl addition of enolates, but the energy differences between boat- and chair-like arrangements are lower for x-sulfinyl carbanions69. Tor tert-butyl sulfoxides only anti- and, vn-products are obtained, arising from the approach onto the same diastereotopic face of the anion, but with different relative topicity. The exchange of lithium by zinc causes an increase of the anft-produci, but attempts to titanate the anion failed (see Table 3)69. 

Lithium and zinc tert-butyl phenylmethyl sulfoxide (1) and A-phenyl imines 2, in which the substituent R is alkenyl or aryl, react at —78 °C over 2 hours with high anti diastereoselection (d.r. >98.5 1.5)6. Shorter reaction times result in poorer yields, due to incomplete reaction. In contrast, the reaction of the sulfoxide anion with benzaldehyde is complete after 5 seconds, but shows poor diastereoselection. When the substituent R1 or R2 of the imine 2 is aliphatic, the substrates exhibit poor chemical reactivity and diastereoselection. The high anti diastereoselection suggests that if a chelated cyclic transition state is involved (E configuration of the imine), then the boat transition state 4 is favored over its chair counterpart 5. 

Larger chalcogen-phosphorus heterocycles, although less common in the literature, are accessible via a variety of synthetic routes.2,83,84 For example, the cyclic trimer (SPR)3 (R = 2,4,6-tri-tert-butylphenyl) contains a puckered six-membered P3S3 ring and is produced in the reaction of a phosphinic chloride with lithium sulfide (Equation 73).98 Additionally (R P)3Se5 (R = 2,4-di-tert-butyl-6-wopropoxyphenyl), synthesised from the oxidation of a primary phosphine with three equivalents of elemental selenium (Equation 74), has... 

Other papers of interest in this section report transamination of camphor-3-carbothioamides with secondary cyclic amines, reaction of camphorquinone with dimethyl /S-ketoglutarate, the use of fenchone (212 X=0) in alkene formation from Grignard reagents, bromination of 2-e/itfo-6-endo-dibromobornane to yield 2,3,6-endo-tribromoborn-2-ene, and camphor-enol trimethylsilyl ether formation by quenching the reaction mixture of butyl-lithium and camphor tosyl-hydrazone with trimethylsilyl chloride. ... 

The formation of -butyldiazoate by reaction of [Fe(CN)5(NO)]2 with lithium -butyl amide contrasts with the formation of dibutylamine as the main product in the reaction of the same complex with -butylamine (85). This can be explained if the diazoic/diazoate equilibrium shown in Fig. 18 is shifted to the left far enough to form of a diazenido by loss of hydroxide. Attack of -butylamine on the a-carbon of the diazenido species, produces dibutylamine. DFT computed results suggest that the stabilization by complexation of the intermediate diazonium ion (see Fig. 18) is large for the iron-pentacyano complex, in agreement with the fact that no rearrangement products were observed in the reaction of this species with -butylamine (86). The reaction has been proposed as a good route for the preparation of symmetrical, unsymmetrical, and cyclic secondary amines (85). 

An eight-membered cyclic 7,./V-bis(germadiyl)bis(ketenimine) 190 was prepared by the reaction of tert-butyl-lithium with (fluorodimesitylgermyl)phenylacetonitrile 188 leading to the lithium salt 189, which then underwent an elimination of lithium halide. Compound 190, the first ring containing two ketenimine moieties, was characterized by IR and 13C NMR spectroscopy as well as X-ray structure determination (Scheme 34) <19980M1517>. 

---