Allyl-lithiums

Henning, F. Lehr, and D. Seebach, Helv. Chim. Acta, 1976, 59, 2213. 

The allene-lithium (27), formed by metallation of methoxyallene, reacts with a-halogenoketones to give epoxides (28), which in turn give furans (29) on reaction with Bu OK in DMSO. Lithiated trimethylsilyl allyl ether (30) reacts with ketones to give 1,2-diol derivatives (31), or cyclizes if there is an appropriate electrophilic centre in the molecule.  

Schreurs, J. Meijer.P. Vermeer,and L. BvdiX dsm2i,TetrahedronLetters, 1976,2387. 

The anion from 3-methylpentadienyl-lithium exists substantially in the conformation (32), and is a useful reagent for introducing a diene unit common to several terpenoid species. Thus, reactionof(32)withR COR gives (33). 1,3-Dilithioalkynes are alkylated regioselectively at the 3-position and can then be reacted with another electrophile at the 1-position.  

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The addition of anhydrous cadmium iodide or chloride on allylic lithium carbanions causes changes in the regioselectivity, but information on the stereochemical results is scarce31-42-43. 

The reaction of the phenylsulphinyl allylic lithium a-carbanion 342 with oxiranes was found by Guittet and Julia to give, after rearrangement and desulphurization, dihydroxy-dienes 343427 (equation 197). Demoute and coworkers have described the alkylation reaction of a very sophisticated 2-alkenyl sulphoxide 344 as a part of the total synthesis of a juvenile hormone 345428 (equation 198). Since the allylic sulphoxide carbanion has an ambident character, the alkylation may occur sometimes also at the y-position. This direction of alkylation is observed in the case of acyclic allylic sulphoxide anions 346, and results in the formation of the corresponding allylic sulphoxide 347 and vinylic sulphoxide 348423 (equation 199). 

This type of metallic exchange is used much less often than 12-32 and 12-33. It is an equilibrium reaction and is useful only if the equilibrium lies in the desired direction. Usually the goal is to prepare a lithium compound that is not prepared easily in other ways, for example, a vinylic or an allylic lithium, most commonly from an organotin substrate. Examples are the preparation of vinyllithium from phenyl-lithium and tetravinyltin and the formation of a-dialkylamino organolithium compounds from the corresponding organotin compounds ... 

Two main structural types have been identified for allyl alkali metal species solvated ions in the form of CIPs where a delocalized anion with metal coordination is perpendicular to the ligand plane,130-134 or unsolvated allylic lithium compounds displaying localized ligand systems with NMR spectra closely resembling those of alkenes.135-138... 

Preparation of allyltitaniums of the type (allyl)Ti(OiPr) 3 from the corresponding allyl-lithium or -magnesium compounds and ClTi(OiPr)3 by transmetallation and their subsequent synthetic utilization have attracted considerable interest because of the advantageous reactivity of the allyltitaniums as compared to other allylmetal complexes in terms of chemo-, regio-, and diastereoselectivity [3], The preparation of certain allyllithium or -magnesium reagents, however, is not necessarily easy, which would seem to limit the utility of this method. 

If the alkenes and acetylenes that are subjected to the reaction mediated by 1 have a leaving group at an appropriate position, as already described in Eq. 9.16, the resulting titanacycles undergo an elimination (path A) as shown in Eq. 9.58 [36], As the resulting vinyltitaniums can be trapped by electrophiles such as aldehydes, this reaction can be viewed as an alternative to stoichiometric metallo-ene reactions via allylic lithium, magnesium, or zinc complexes (path B). Preparations of optically active N-heterocycles [103], which enabled the synthesis of (—)-a-kainic acid (Eq. 9.59) [104,105], of cross-conjugated trienes useful for the diene-transmissive Diels—Alder reaction [106], and of exocyclic bis(allene)s and cyclobutene derivatives [107] have all been reported based on this method. 

Addition of l,3-bis(methylthio)allyllithium to aldehydes, ketones, and epoxides followed by mercuric ion-promoted hydrolysis furnishes hydroxyalkyl derivatives of acrolein5 that are otherwise available in lower yield by multistep procedures. For example, addition of 1,3-bis-(methylthio)allyllithium to acetone proceeds in 97% yield to give a tertiary alcohol that is hydrolyzed with mercuric chloride and calcium carbonate to saturated aldehyde.8 Similarly, addition of l,3-bis(methylthio)allyl-lithium to an epoxide, acetylation of the hydroxyl group, and hydrolysis with mercuric chloride and calcium carbonate provides a 5-acetoxy-a,/ -unsaturatcd aldehyde,6 as indicated in Table I. Cyclic cis-epoxides give aldehydes in which the acetoxy group is trans to the 3-oxopropenyl group. 

Cycloadditions of this type do not occur with isolated non-activated C-C double bonds, the 2-azaallyl system (Scheme 3) is only capable of existence with stabilizing aromatic groups and the allyl-lithium stem (Scheme 3) has no tendency at all to undergo cycloaddition, if a group is lacking which can stabilize the negative charge in the 2-position ... 

We asked the question if it is possible to replace the phenyl residues which are parts of the reagents of Scheme 3 by organoelement groups. On these groups we make the following demands They should be electron withdrawing and resistant to the attack of 2-azaallyl-lithium, of allyl-lithium compounds, of water, and of oxygen as well. Moreover they should be easily removable after the cycloaddition. 

Reaction of BTSP with 2-benzothiazolyl allyl lithium proceeds in a regioselective and stereoselective manner leading to the silyloxylation and the trans methylation product (Scheme 9). 

The absence of a-alkylated allylic sulfoxides or the corresponding 2,3-sigmatropically rearranged allylic alcohols as well as of y-alkylated vinylic sulfoxides supports the intermediacy of a vinylic rather than an allylic lithium species. 

Aza-allyl-lithium-Verbindungen lassen sich auch durch schwaches Erhitzen der N-Li-thium-Derivate einiger Aryl-aziridine (z.B. 2,3-Diphenyl-aziridin) erhalten und danach bei tiefen Temperaturen mit geeigneten Ethen-Derivaten (z.B. 1,2-Diphenyl-ethen, Phen-ylthio-ethen) zu Pyrrolidinen umsetzen1-2. 

Alkyl-bromide (bzw. Allyl-bromid) sowie Ketone reagieren mit dem aus Benzophenon-methylimin und Lithium-diisopropylamid gebildeten l,l-Diphenyl-2-aza-allyl-lithium un-ter Substitution zu l-(Diphenylmethylen-amino)-alkanen bzw. l-(Diphenylme-thylen-amino)-2-hydroxy-alkanen, deren saure Hydrolyse 1-Amino-alkane bzw. 1-Ami no-2-hydroxy-alkane ergibt1. 

The association states of the benzylic- and allylic-lithium active centers have been studied by viscosity, light scattering and cryoscopy (Table 2). The majority of results indicate that the dimeric state of association is present for these active centers at the concentrations appropriate for polymerization (10-3 to 10-4 M). 

Furthermore, several of Worsfold s assessments seem to be open to question. The assertion that the association (between the allylic-lithium active centers) is between ionic species can be contrasted with the evidence provided by NMR spectroscopy 36,134 143) which has shown that the carbon-lithium bond of allylic-lithium species can possess considerable covalent character. Worsfold has also previously published 43 > concentrated solution viscosity results where the ratio of flow times, before and after termination, of a poly(isoprenyl)lithium solution was about 15. This finding is clearly incompatible with the conclusion that viscometry cannot detect the presence of aggregates greater than dimeric. 

The alteration in solution viscosities brought about by the conversion of the allyllic-lithium active center to the alkoxy-lithium species is in accord with the general trend 148,1491 observed for star-shaped polymers in concentrated solution. It must be noted though that viscosity measurements cannot generally be used to detect differ-... 

Hay and co-workers reported that the Mn increased linearly with conversion at a molar ratio of 1 2. However, at high ratios of n-BuLi to TMEDA, the initiator became only 50% efficient. This finding is rather surprising as the addition of TMEDA to alkyllithium compounds enhanced the rate of the polymerization and without TMEDA, at Hay s polymerization temperature, no polymerization of the 1,3-butadiene took place. The explanation advanced by these authors was that the allylic lithium complex of polybutadiene is complexed with two TMEDA molecules and that complex 11 is the propagating species. 

As may be seen from Fig. 3, there are no resonance peaks at 120-128 ppm characteristic of 1,4-microstructure in polybutadiene polymer. However, on addition of methanol to the chain live ends, resonance peaks at 120-128 ppm appear in ratios of 60% trans-1,4, 14% m-1,4, and 26% 1,2. This suggests that the protonation of the chain live ends with methanol is an independent reaction and does not relate to the actual structure of the propagating species. It may be said that the structure of the allylic lithium of polybutadiene (DP > 1) is postulated to exist in the 1,2-form (13). Yet hydrolysis of 13 gives mixed 1,4- and 1,2-microstructures. 

The polymerization of 1,4-butadiene and related conjugated dienes in polar media was discussed earlier. The major focus of this part of the review will be devoted to the polymerization of 1,3-butadiene and iso-prene in hydrocarbon media, with emphasis on the allylic lithium structure and reactivity. 

The reaction of tri(substituted allyl) stannyllithium with (substituted allyl)lithium formed an equilibrium mixture of tri(substituted allyl) stannyllithiums having all possible combinations of substituents (equation 196)204. 

Catalytic DBB29 avoids the need for such vigorous conditions, and allows benzyl48 and allyl lithiums to be formed from silyl ethers,49 mesylates50 triflates,51 carbamates and carbonates,9 and even directly from lithium alkoxides.49... 

Waak 15) also used other unsaturated lithium organic initiators (such as allyl-lithium, crotyllithium) for styrene polymerization. Though more efficient than vinyllithium, these initiators exhibit the same disadvantages. Therefore, the same conclusions apply. 

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