.alpha.-Haloallyllithium species. Coupling with alkyl bromides

Macdonald, Timothy L.; Narayanan, B. A.; O'Dell, Dale E.

doi:10.1021/jo00320a058

Cited by 34 publications

(9 citation statements)

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“…Allyl chloride 5 was made by the method reported previously, which involves the regio- and stereospecific alkylation of trans -1-chloro-2-hexene with 1-bromobutane. The alkylation is carried out at −78 °C and requires introduction of the hindered strong base, ( i -Pr) 2 NLi . In order to synthesize 6 , the sequence shown in eqs 2−4 was used.…”

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confidence: 99%

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Six-Center Concerted Mechanism for Poly(vinyl chloride) Dehydrochlorination. Requiescat in Pace?

1996

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“…The alkylation is carried out at -78 °C and requires introduction of the hindered strong base, (i-Pr) 2 NLi. 7 In order to synthesize 6, the sequence shown in eqs 2-4 was used. Here the preparation of alcohol 8 via 7 was adapted from published procedures 8 for the conversion of 1-alkynes into β-hydroxy-transalkenes.…”

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confidence: 99%

Six-Center Concerted Mechanism for Poly(vinyl chloride) Dehydrochlorination. Requiescat in Pace?

1996

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“…Metalation and alkylation of alkyl halides at the a position can, therefore, usually only be performed when this position is activated by an additional electron-withdrawing group, and b-elimination is either not possible or difficult. The metalation of allylic [187,[304][305][306][307][308] or propargylic [309] chlorides or bromides can be performed at low temperatures, and addition of Lewis acids can enable highly stereoselective alkylations with these carbanions (Scheme 5.34). 2-Haloacetic esters [293,294], 2-haloacetic thiolesters [295], 4-halocrotonic acid esters [123], 2-(1-haloalkyl)oxazolidines [292,[296][297][298], a-halo ketones [299], a-halo sulfoxides [300,301], and a-halo imines [302,303] can all be metalated and alkylated at low temperatures without loss of halide from the nucleophile.…”

Section: A-halogen Carbanionsmentioning

confidence: 99%

The Alkylation of Carbanions

Dörwald

2004

Side Reactions in Organic Synthesis

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The deprotonation of organic compounds by strong, non-nucleophilic bases followed by C-alkylation with a suitable electrophile has become one of the most predictable and straightforward methods for formation of C-C bonds. The popularity of this chemistry is also a consequence of the often-seen close resemblance of feasible structural modifications by a deprotonation/alkylation strategy to an unsophisticated retrosynthetic analysis of a given target compound. Other reactions, which involve, for instance, substantial rearrangement of the carbon framework (e.g. Cope rearrangement, fragmentations, ring contractions or enlargements) are usually more difficult to take into account during retrosynthetic analysis.LDA and related, sterically hindered, lithium dialkylamides, first investigated by Levine [1], have completely replaced the more nucleophilic sodium amide, which had been the base of choice for many years [2]. Because the reactivity of an organometallic compound depends to a large extent on its state of aggregation (i.e. on the solvent and on additives) and on the metal, transmetalation of the lithiated intermediates and the choice of different solvents and additives emerged as powerful strategies for fine-tuning the reactivity of these valuable nucleophiles.In this chapter the alkylation of carbanions with simple carbon electrophiles will be discussed, with special emphasis on the structure-reactivity relationship of the carbanion and on side reactions. In this context the term "carbanion" refers to an intermediate prepared by in-situ deprotonation of an organic compound, followed by optional cation exchange (transmetalation), which tends to be alkylated at carbon by soft electrophiles such as MeI or PhCHO. This type of reactivity is characteristic of enolates with an ionic M-O bond or for organometallic compounds with a strongly polarized or ionic M-C bond, M typically being an alkali metal, Mg, Cu, or Zn. Carbanions can, alternatively, also be prepared by halogen-metal exchange [3-8], sulfoxide-or sulfone-metal exchange [9-13], or by transmetalation of stannanes. The most suitable reagents for performing such metalating exchange reactions are organometallic compounds with a metal-bound secondary or tertiary alkyl group, such as tBuLi, sBuLi, iPr 2 Zn [14, 15], or iPrMgHal [6]. These reagents are thermodynamically less stable than organometallic compounds with primary alkyl 5 146 Scheme 5.1. Approximate relative rates of proton transfer in water at thermoneutrality (DpK a = 0) [35, 39, 51]. 147 Scheme 5.2. The effect of fluorine on the acidity of organic compounds [24, 62-65]. 148 Scheme 5.3. Dependence of the reactivity of carbanions on their basicity [68, 72-74]. Regioselectivity of Deprotonations and AlkylationsThe organic chemist is occasionally confronted with the problem that a compound has several differrent X-H groups of similar pK a . If only one of these is to be alkylated, one option would be to perform a regioselective deprotonation. This can sometimes be achieved by exploiting small differences be...

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“…Kharasch's examination of halogen-substituted allyl anions in 1939 provided the first examples of heterosubstituted allylic species to be studied . Analogous to the corresponding bromides, allyl chlorides 4 undergo α-alkylation to 7 with aliphatic halides 7 and TMSCl (Scheme ). , Such sequences were, for example, used for the preparation of lavanduol 9 and pheromones . Similarly, 1-chloro-1-methylallyllithium 19 reacts with aldimines and ketimines via attack at the α-carbon to produce N-substituted ethylenic aziridines 20 .…”

Section: Allyl Chlorides (Cc−c−cl)mentioning

confidence: 99%