Quenching electrophilic

Stannylation, followed by trans-metallation and subsequent electrophilic quenching, provides a good route (6) to simple functionalized vinylsilanes ... 

Scheme 4.8. Hydrozirconation and electrophilic quenching of alkynyl sulfoxides.

Electrophilic fluorinating agents, 77 847 Electrophilic quench, 72 828 Electrophilic reactions... 

In 1991, Park reported123 the first synthesis of iron alkynylcarbene complexes (184), involving the nucleophilic attack of a lithium acetylide on pentacarbonyl iron, followed by electrophilic quench. With such compounds in hand, he proceeded to investigate their reactivity123,124 and found that upon addition of cyclopentadiene to the alkynylcarbene complexes 184, the products formed were 774-vinylketene complexes (185). During column chromatography, some of these products (185.a and 185.b) were transformed into the tricarbonyl(norbornadiene)iron derivatives 186. Others (185.C and 185.d, not shown) were hydrolyzed as part of the workup procedure, to afford pure samples of the norbornadiene complexes 186.C and... 

The biphenyl diamide 171 also displays diastereoselectivity in its ortholithiation-electrophilic quench, giving the C2-symmetric, chiral diastereoisomer of the diamide 172 . 

Among derivatives of acetophenone, the acetal 399 (R = Me) perfonns the best . Lithiation with f-BuLi in THF and electrophilic quench gives 402a in 60-85% yield and with about 95 5 diastereoselectivity (Scheme 166). Switching to Et20 as the solvent leads to a precipitate which reacts with completely reversed diastereoselectivity, giving 402b. 

THF at —30°C followed by electrophilic quench with 1,2-dibromoethane, for example, yields the product 406 with no trace of its diastereoisomer (>99.5 0.5 selectivity) in 64% isolated yield. 

By careful optimization, Widdowson and coworkers were able to show that methoxy-methyl ethers of phenols are better substrates for alkyllithium-diamine controlled enan-tioselective deprotonation, and (—)-sparteine 362 is then also the best ligand among those surveyed the BuLi-(—)-sparteine complex deprotonates 447 to give, after electrophilic quench, compounds such as 449 in 58% yield and 92% ee (Scheme 180) . Deprotonation of the anisole complex 410 (see Scheme 169) under these conditions gave products of opposite absolute stereochemistry with poor ee. 

The carbamates 549 (R = OBu-f) behave similarly, though they must be lithiated with i-BuLi to avoid addition to the carbonyl group °. It is possible simply to use a lithium carbamate to protect an amino group during a lateral lithiation an initial deprotonation and carbonation generates the lithium carbamate 556, which is then deprotonated twice more by t-BuLi (Scheme 220). After electrophilic quench, acid hydrolysis of the carbamic... 

By carrying out a subsequent ortholithiation at low temperature, it was possible to show that tertiary benzamides also react atroposelectively in laterally lithiation-electrophilic quench sequences . Either atropisomer 575 or 578 could be made starting from 573 or 576 (Scheme 231). 

Stereoselective deprotonation of componnd 581 is possible (Scheme 233), bnt the yields and enantioselectivities obtained are poorer than for the chromium-complexed analogues (see below). With an internal electrophilic quench it was possible to form the axially chiral benzamide 582 in 89% ee using hthium amide 360 . 

Although there is a kinetic barrier to the direct deprotonation of tertiary amines, Ahlbrecht and Dollinger showed in 1984 that the Schlosser superbase, i c-BuLi/f-BuOK, can deprotonate A-methylpiperidine selectively on the methyl group (Scheme 3). This superbase probably yields an a-amino-organopotassium species (and f-BuOLi), but treatment with LiBr effects transmetalation to the more nucleophilic, and less basic, a-amino-organolithium species. Electrophilic quench with several aldehydes and ketones gives substitution products in good yields as typified by the example in Scheme 3. Similarly,... 

Recently, some examples of the dearomatizing cyclization of unstabilized a-amino-organolithium compounds have been reported. For example, Clayden and Kenworthy showed that cyclization onto an oxazoline-activated naphthalene ring gives a lithium azaenolate. Note the high diastereoselectivity of the subsequent electrophilic quench, which places the electrophile cis to the carbon-carbon bond formed in the cyclization step (Scheme 25). "... 

A greatly improved experimental procedure for the synthesis of thieno[2,3-d]-1,2,3-thiadiazole caiboxylates 68 was reported by Stanetty et al. and involved diazotisation of aminothiophene derivatives 67 <99JHC761>. In these systems, substituents could be introduced into the 5-position by nucleophilic displacement of a chlorine atom or by metallation of the unsubstituted compound (68 R = H) and subsequent electrophilic quenching <99JPR391>. 

In the sole case studied, LiTMP deprotonation of 2-chloropyrazine (112) followed by electrophile quench gave the 3-substituted derivatives 113 in good yields (Scheme 34) (88S881). 

That the combined DMG effects of OMe and N-pivaloyl are not necessary was demonstrated by the metalation of the simple 2-, 3-, and 4-N-pivaloyl pyridines 203 to give, after electrophile quench, products 204 (Scheme 61) (82S499 83JOC3401 89JHC105). Using n-BuLi (2.5 equiv./ TMEDA/Et20/ - 10°C) or n-BuLi (2.5 equiv./THF/0°C) conditions, a variety of substituted amino pyridines 205-207 were thereby prepared. In all cases, regiospecific metalation at the most acidic site was observed. For example, metalation of the 3-N-pivaloyl isomer 203 at -40°C occurred at... 

OSEM pyridine (313) [90TL4267]. Metalation followed by electrophile quench leads to derivatives 314. Using 4-TMS protection, a tactic developed in aromatic amide DoM chemistry (90CRV879), further metalation of... 

TMS derivative 314 and electrophile quench afford compounds 316, which can be selectively C-4 desilylated to give product 315 (Scheme 95). 

The 3-pyridyl O-carbamate affords, under the sec-BuLi/TMEDA conditions, only 4-substituted products. A reinvestigation of LDA metalation (85JOC5436) has shown that high-yield conversion of 320 into the 4-TMS (319) and 2,4-bis-TMS (321) derivatives can be effected (Scheme 97) [90UP1]. Furthermore, LiTMP metalation of 319 followed by electrophile quench leads to derivatives 322, thus demonstrating the TMS protection route to 2-substituted 3-oxygenated pyridines. Another, potentially useful result is the 2-position selective ipso carbodesilylation of 321 with benzoyl chloride, yielding 323. 

In a series of studies concerning the application of DoM reactions to the synthesis of furoquinoline alkaloids (see Section VIII), Narasimhan and co-workers effected the model metalations of 2-ethoxyquinoline (332) to give, after electrophile quench, low yields of 3-substituted products 335... 

In this as yet poorly investigated area, LiTMP metalation of 2-methoxy and 2,6-dimethoxypyrazines 389 and appropriate electrophile quench has been shown to give products 390 (Scheme 119) (90JOC3410, 90TH1 91JOM). 

In l,2,3-triazolo[5,l-a]isoquinoline (520), the N-3 atom appears to direct metalation to the peri C-4 position, as seen from the products 521 derived from electrophile quench experiments (Scheme 158) [85JCS(P1)1897]. With TMSC1, besides 60% of 521 (E=TMS), 23% of 1,5-disubstituted... 

Given that this was apparently the first time an enantiomerically enriched benzyllithium had been made using a chiral lithium amide base, we tried trapping it with an external electrophile. Only by carbonation did we manage to obtain any enantioselectivity in the product 41 (Scheme 11) slower electrophilic quenches (such as, evidently, methyl iodide) presumably allow time for organolithium to racemise.48... 

It is important to end-cap the living carbosilane polymer with 1,1 -diphenylethylene to decrease the reactivity of the living center in order to obtain the block copolymer successfully. The diphenylethylene thus provides a milder carbanion for initiation of the methacrylate monomer. With this modification, efficiency of the end-capping by an electrophile (quenching) has reached 0.95 <2001PSA86, 1998PSA2699>. 

The advantage of in-between DoM followed by sequential intramolecular trapping of the incipient benzyne and electrophile quench, 46 —>47 (Scheme 11) constitutes a powerful method in heteroaromatic synthesis [35],... 

The deprotonation and electrophilic quench of unfunctionalised allylic compounds provides a useful way of making functionalised Z-alkenes, since the intermediate allylmetal species prefers the endo configuration.281-19 For example, 1-dodecene 501 can be transformed in 57% yield to Z-dodecenol 502 on a 15 g scale.281... 

Unlike allyllithiums, the allylceriums prefer the trans configuration, so warming the intermediate 111 after transmetallation but before electrophilic quench leads to trans alkenes such as , -112. 

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