Alkenyl lithium compounds

Just one reaction has been described where lithiated methoxyallene 42 reacted with bicyclo[3.2.0]heptenone 175 to form the triquinane derivative 176 via a tandem oxy-Cope-transannular ring closure sequence (Eq. 8.31) [111]. However, cycloocta-none 177 was isolated as a major product, which is unusual since other alkenyl-lithium compounds and 175 provide only triquinanes. The authors assumed that the additional sp2-hybridized C-atom in the eight-membered ring intermediate (eno-late of 177) induces a conformation which is less susceptible to transannular ring closure. 

Fig. 16.16. Stereoselective preparations of cis-alkenyl-boronic acids and the corresponding diisopropyl ester starting with cis-bromoalkenes. The first step involves a Br/Li exchange to form the alkenyl-lithium compound B. This organolithium compound is subsequently transmetalated to give complex C by using B(0/Pr)3.

Figure 3 Li chemical shifts for alkyl and alkenyl lithium compounds in different solvents relative to 0.1 M LiBr as external reference. (Reprinted with permission from ref. [49]. Copyright (1974) American Chemical Society)...

A novel approach to 2-amino-1,3-butadienes 10 was recently presented by Enders, Hek-ker and Meyer. [30] The synthesis was accomplished by a two step one pot procedure by coupling the alkenyl lithium compounds 8... 

Indeed, as shown in Scheme 31, highly diastereoselective crotylzincation of t-butoxy-substituted Z-alkenyl lithium affords. sy 3-geminated organodimetal compound with high diastereoselectivity41. Once the alkenyllithium has a secondary allylic substituent, three... 

Alkenyl, alkynyl, and aryl halides, like alkyl halides, can be converted to the corresponding magnesium and lithium compounds. However, the reaction conditions, such as choice of solvent, can be critical. Bromoethene, for instance, can be converted to ethenylmagnesium bromide in good yield if the solvent is oxacyclopentane [tetrahydrofuran, (CH2)40] ... 

The most stable structures of alkyl and alkenyl anions predicted with the VSEPR theory are supported by reliable calculations. There are no known experimental structural data. In fact, up to recently, one would have cited the many known geometries of the lithium derivatives of these carbanions as evidence for the structure. One would simply have dropped the C—Li bond(s) from these geometries. However, it is now known that the considerable covalent character of most C—Li bonds makes organo-lithium compounds unsuitable models for carbanions. 

One example was also reported showing the formation of an (El-alkenyl sulfoxide in the reaction of a vinylic lithium compound on menthyl sulfinate (eq 4). ... 

Lithium hexamethyidisilazide. 13, 165 14 Alkenyl sulfur compounds. Diethyl... 

Enantioenriched 3-(trialkylstannyl)alkenyl carbamates are accessible from the lithium compound (S)-265a in both enantiomeric forms [ 173]. These can be kept for several days in the refrigerator. Metal exchange with titanium tetrachloride in the presence of an aldehyde or ketone generates the highly reactive a-trichlorotitanium intermediate 312, leading to homoaldol adducts 314 or ent-314, respectively. From the configuration of these adducts it is concluded that the... 

The boron compound can be a borane (R jB), a borate ester (R -B(OR)2), or a boric acid (R -B(OH)2), where R is an allqrl, alkenyl, or aryl group. Boranes are made using hydroboration of alkenes or allgmes. Borates are made from aryl or alkyl lithium compounds and trimethyl borate. 

For example, with the organotin compound having hetero atoms the transmetalation proceeds easily by the stabilization effects of hetero atoms. Then, the lithium compounds react with alkenyl halides and are hydrolyzed to give naturally obtainable 9-hydroxydendrolasin [75]. 

Reductive cleavage of sulphides, selenides, and tellurides on Raney nickeP and cleavage by lithium in THE, leading to secondary or tertiary alkyl-lithium compounds, are useful synthetic operations novel variations are involved in the cleavage of dialkenyl sulphides with EtjSiH (giving low yields of silyl sulphides) and of alkenyl, aryl, and allyl sulphides and selenides with PPhj and... 

PhS(0)(0Ph)Me + RLi and LiX - PhSOCH X + PhSO Me]/ or reduction with homologation (with RjCuLi and LiX)/ Standard sulphinylation procedures reported include electrophilic substitution of phenols with ArSOCl and AlClj and the preparation of optically active sulphoxides from resolved (—)-menthyl sulphinates with ( )-l-alkenylmagnesium bromides or arylthiomethyl- or arylsulphonylmethyl-lithium compounds/ A practical route to 1-alkenyl sulphoxides uses non-activated alkynes and sulphenic acids, generated in situ from the thermolysis of 2-cyanoethyl phenyl sulphoxides/ ... 

Homologation of aldehydes can be achieved by reaction of the anion (26) with the aldehyde, metallating with BuLi, and hydrolysing the intermediate thus obtained. " The alkenyl-lithiums (27) and (28) provide routes to functionalized carbonyl compounds, both cyclic and acyclic, on reaction with a variety of conventional electrophiles. By employing bulky substituents at the carbonyl group of the enones (29a and b), a -activity is enforced. Lithium amides may be carbonylated to give the corresponding carbamoyl-lithiums (30), which are useful acyl anion equivalents. ... 

Aldehydes (RCHO) react with 1-diazo-l-lithioacetone to give a-diazo- -hydroxyketones (48). These latter compounds can then be converted to P-diketones by the addition of rhodium(il) acetate a procedure which has been applied in the synthesis of -damascone. 1,6,6A -Trithiapentalene and a metal salt catalyse the lithiation of unactivated alkenes to alkenyl-lithiums by lithium metal, constituting a very useful method for preparing such compounds since in the past the preparation of alkenyl-lithiums from lithium metal has been confined to alkenes containing relatively acidic protons. Finally, the allenyl-lithium reagent (49) can be converted to various functionalized allenes by simple electrophiles. ... 

Conjugate addition of cis- or /ra 5-l-alkenyl-lithium cuprates (R—CH= CH—jgCuLi to a/5-unsaturated carbonyl compounds also occurs with high retention of double-bond geometry, affording isomerically pure cis- or trawj-yd-ethylenic carbonyl compounds (Scheme 20). ... 

The versatility of lithium aluminum hydride permits synthesis of alkyl, alkenyl, and arylsilanes. Silanes containing functional groups, such as chloro, amino, and alkoxyl in the organic substituents, can also be prepared. Mixed compounds containing both SiCl and SiH cannot be prepared from organopolyhalosilanes using lithium aluminum hydride. Reduction is invariably complete. 

Organolithium reagents (Section 14.3) Lithium metal reacts with organic halides to produce organolithium compounds. The organic halide may be alkyl, alkenyl, or aryl. Iodides react most and fluorides least readily bromides are used most often. Suitable solvents include hexane, diethyl ether, and tetrahy-drofuran. 

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