By organolithium reagents

Carbamate substituents have also been found to permit the direct removal of allylic, propargylic and allenic protons by organolithium reagents [32, 33]. In the latter case, the resulting lithioallenes can be converted to the allenyltitanium reagents with ClTi(OiPr)3 (Eq. 9.28) [8]. As illustrated, subsequent addition to acetaldehyde proceeds with only modest diastereoselectivity. 

An ab initio study of the energetics of deprotonation of cyclic vinyl ethers by organolithium reagents has clarified the ring-size-dependent competition between vinylic and allylic deprotonation.The respective transition states involve preequilibrium complexation of lithium to the electron-rich vinyl ether oxygen, prior to deprotonation via a multi-centre process free ions are not formed during the lithiation. 

Several examples of intramolecular additions to carbonyl groups by organolithium reagents generated by halogen-metal exchange have been reported, such as the examples shown below. What relative reactivity relationships must hold in order for... 

Trialkylated borazines R3B3N3H3 are deprotonated by organolithium reagents, but other reaction pathways also occur.For example, the reaction of Me3B3N3H3 with one equivalent of methyllithium produces the solvated monolithium derivative [(Me3B3N3H2)Li(OEt2)]2 (9.9), which is dimeric in the solid state. The formation of di- or trilithiated derivatives. 

Dithianes are ring opened by organolithium reagents and subsequent reaction with electrophiles provides unsymmetrically substituted dithia compounds (95JCS(P1)2381). 

The addition compounds (I) are insoluble in diethyl ether, and the slurries obtained are quite stable. In more strongly solvating media, such as tetrahydrofuran or dimethoxyethane, the compounds are soluble but show rapid decomposition, with trimethylamine and polymethylene as the main products. These experiments indicate (9, 40) that when the lithium salt is trapped by donor solvent molecules, the free ylide quickly undergoes decomposition (40). No free trialkylammonium ylide has yet been prepared, even under very mild conditions (35). On the other hand, it has been shown, that the tetramethylammonium cation can even be metalated twice by organolithium reagents (102) to afford dimethyl-ammonium bismethylides ... 

Ferrocene derivatives containing a single disulfide link are occasionally obtained from reactions of fc(SH)2, e.g., with norbornene [84] or with the oxonium salt [(Ph3PAu)30]BF4 (Scheme 5-18) [90]. Splitting of l,2,3-trithia-[3]ferrocenophane, fc(S3), by organolithium reagents followed by air oxidation is another pathway to disulfides (Scheme 5-51) [95]. 

Some amide chlorides such as 37 , 38 can be transformed into amino derivatives by organolithium reagents (equations 73 and 74 ). 

Cleavage of As—As bonds by organolithium reagents PhLi reacts with As—As bonds to give monolithium arsenides (equation 181 ). 

T.3.3 Correlate reaction the reaction of telluronium salts with carbonyl compounds mediated by organolithium reagents - formation of secondary alcohols... 

The crystal and molecular structures of 105 have been determined it has an anomalous structure with very short intermolecular Te—N bonds of 2.4 A.159 Mass spectral,28 13C- and 77Se-NMR data160 of 1,2-benzisoselen-azoles have been reported. The intramolecular Se—N bond in these compounds is weaker than in 1,2-benzisothiazoles and is readily cleaved by organolithium reagents.161162... 

Table 8.29. Nucleophilic Aromatic Substitution of 733 by Organolithium Reagents and Enolate Anions...

Silicon is also the preferred site of attack by organolithium reagents on 2,5-dihydrosiloles (e.g. (58)) and leads to formation of ring opened polymers (59) <87JOC4489>. However, if the silicon substituents are sufficiently bulky as in (60) then deprotonation to the anion (61) predominates. Subsequent reaction of (61) with electrophiles (E) can occur either at position two (62) or at position four (63). In the case of protonation the 2,5-dihydrosilole (62 E = H) is virtually the sole product, but with larger electrophiles rather more of (63) than of (62) is formed. 

All of the M—M bonds may be cleaved by organolithium reagents, but differences in reactivity are not at present apparent. In view of the results cited above for lithium and the hexaalkyl derivatives, a similar trend may be expected with these latter compounds and organometallic reagents. 

These observations, added to the fact that addition of polar solvents to polymerization reactions of butadiene initiated by organolithium reagents in hydrocarbon solvents can change the stereochemistry from one of predominantly rtr-1,4 to that of 1,2 and trans-, , suggests that the lithium may form a tt complex with the olefin, and if this is sufficiently strong, orient the monomer prior to the incorporation step. 

Richter and Neufler and more recently Vogt and co-workers studied the mono- and disubstitution of the menthoxy groups on phenylmenthylpho-sphonite (70) by organolithium reagents (Scheme 2.25), without any protecting group involved. 

Scheme 4.3 Nucleophilic ring opening of 7 by organolithium reagents.

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