Lithium metal intermediates

From intermediate 12, the path to key intermediate 7 is straightforward. Reductive removal of the benzyloxymethyl protecting group in 12 with lithium metal in liquid ammonia provides diol 27 in an overall yield of 70% from 14. Simultaneous protection of the vicinal hydroxyl groups in 27 in the form of a cyclopentanone ketal is accompanied by cleavage of the tert-butyldimethylsilyl ether. Treatment of the resultant primary alcohol with /V-bromosuccini-mide (NBS) arid triphenylphopshine accomplishes the formation of bromide 7, the central fragment of monensin, in 71 % yield from 27. 

The completion of the synthesis of key intermediate 2 requires only a straightforward sequence of functional group manipulations. In the presence of acetone, cupric sulfate, and camphorsulfonic acid (CSA), the lactol and secondary hydroxyl groups in 10 are simultaneously protected as an acetonide (see intermediate 9). The overall yield of 9 is 55 % from 13. Cleavage of the benzyl ether in 9 with lithium metal in liquid ammonia furnishes a diol (98% yield) which is subsequently converted to selenide 20 according to Grie-co s procedure22 (see Scheme 6a). Oxidation of the selenium atom... 

We examined a variety of dihalosilanes using ultrasonic waves and alkali metals(37). The mild conditions permitted led to fewer products than are normally observed in these reactions and the first evidence that silylenes can be important intermediates in metal-dihalosilane reactions in solution. Our results for some dichlorosilanes reacting with lithium metal are summarized below. 

Another synthetic route which gives a good yield of the labelled tin hydride involves the hydrolysis of an organometallic intermediate such as a trialkylstannyllithium46 with deuterated or tritiated water. The trialkylstannyllithium can be prepared by treating the trialkyltin chloride with lithium metal in THF46. This process is shown in equation 42. 

Lithium carbonate is obtained as an intermediate product in recovery of lithium metal from its ore, spodumene (See Lithium). It is prepared by mixing a hot and concentrated solution of sodium carbonate with lithium chloride or sulfate solution. 

Isocyanates can be used as the source of the N(3)-C(4) unit by reaction with organometallic intermediates. For example, the reaction of ethyl 2-(bromophenyl)imidates 875 with lithium metal, followed by quenching of the lithiated intermediate 876 with phenyl isothiocyanate gave 3-phenyl-2-substituted 4(3//)-quinazolinethiones 877 <1996SC3167>. 

Lithium metal or alkyllithium derivatives react with dihalocyclopropanes to provide the corresponding lithiohalocyclopropanes I which are stable at temperatures around —100 °C. These metalated species are easily trapped with electrophiles (R—X) like methyl or ethyl iodide, trimethylstannyl chloride, tri-methylsilyl chloride etc. In the case of the unsaturated bicyclic substrate II a double bond migration is observed, which in the presence of excess starting bromide is accompanied by isomerization of the axo-lithio intermediate III to its endo-isomer IV [58],... 

Various examples of the use of dissolving metal reduction on exocyclic double bonds, conjugated either with another C —C double bond53 or a carbonyl group,54 have been reported. For example, reaction of 2,6,6-trimethyltricyclo[5-4.0.0I,5]undec-7-en-9-one with lithium metal in liquid ammonia gave, after trapping of the intermediate enolate, 2,6,6-trimethyl-9-tri-fyloxy[5.4.0.015]undec-8-enc (3).53... 

Alkali metal alkyls, particularly n-butyl lithium, are the most frequently used reagents to form metallated intermediates.246 247 In certain cases (di- and triphenyl-methane, acetylene and 1-alkynes, cyclopentadiene) alkali metals can be directly applied. Grignard reagents are used to form magnesium acetylides and cyclopenta-dienyl complexes.248 Organolithium compounds with a bulky alkoxide, most notably M-BuLi-ferf-BuOK in THF/hexane mixture, known as the Lochmann-Schlosser reagent or LICKOR superbase, are more active and versatile reagents.249-252... 

Scission of the cyclopropane rr-bond is also observed in the intermediate cyclopropyl-methyl dilithio derivative obtained from 2-cyclopropyl-1,1-diphenylethylene upon reaction with lithium metal affording the open-chain dilithio-diphenylpentenyl salt (equation 41)91. Again, no experimental evidence for the presence of such intermediate was found though the analogous dilithioalkyne derivative was observed (see below)91. 

Tamborski and coworkers236 found that the reaction of Pl GeCl and lithium metal in THF involved the intermediate formation of Ph3GeGePh3 and resulted in Ph3GeLi. 

The preparation of cychc polysilanes from dialkylchlorosilanes and lithium metal in tetrahydrofiiran presumably involves a sihcon—hthium intermediate (125). 

Cycloaddition of diazomethane to phospholes is a key step in the synthesis of the homophospholes (189). A simple route to phospholyl anions is offered by the reaction of the zircona-cyclopentadienide (190) with phosphorus trichloride, giving the intermediate chlorophosphole (191) which, on treatment with lithium metal, gives the related phospholyl derivative (192). ... 

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