The mechanism of the lithium - halogen Interchange reaction : a review of the literature

Bailey, William F.; Patricia, Jeffrey J.

doi:10.1016/0022-328x(88)83017-1

Cited by 231 publications

(84 citation statements)

References 137 publications

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“…Furthermore, the reaction with dihalides or other electrophiles carries the risk of metal ion halide exchange reactions 40 and/or alkyl halide elimination reactions giving terminal vinyl aromatic (i.e., styryl) end groups in addition to the coupled product (Scheme 2, eqs 6-8). Like naphthalene, the presence of such impurities in the PS cycles may give UV and fluorescence results that are misleading (discussed later).…”

Section: Psmentioning

confidence: 99%

Synthesis and characterization of macrocyclic vinyl aromatic polymers

Hogen‐Esch

2006

J. Polym. Sci. A Polym. Chem.

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The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006

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Section: Psmentioning

confidence: 99%

Synthesis and characterization of macrocyclic vinyl aromatic polymers

Hogen‐Esch

2006

J. Polym. Sci. A Polym. Chem.

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“…An obvious mechanistic proposal to account for the formation of this structure envisions lithium-halogen exchange (5)(6)(7)(8) leading to 12a and methyl bromide (Fig. 3).…”

Section: Resultsmentioning

confidence: 99%

Stereospecific cis- and trans -ring fusions arising from common intermediates

Townsend

Ross

2014

Proc. Natl. Acad. Sci. U.S.A.

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Highly concise and stereospecific routes to cis and trans fusion, carrying various functionality at one of the bridgehead carbons, have been accomplished. Diels-Alder cycloaddition | cyclobutenone | angular methylation | mechanistic studies O ur group has been studying the synthetic utility of the DielsAlder (DA) reaction of the parent cyclobutenone, 2 (1). Recently reported results demonstrate that 2 is a highly reactive, endo-selective dienophile (Fig. 1, Eq. 1) (2). We have also developed a series of intramolecular Diels-Alder (IMDA) reactions, wherein the cyclobutenone component is tethered to various conjugated dienes (compare 4); cycloaddition of these substrates delivers adducts of the type 5, which can be readily converted to trans-fused systems bearing iso-DA patterns (Fig. 1, Eq. 2, 5→6) (3). Additionally, we have described the synthesis and DA cycloaddition of an even more powerful dienophile, 2-bromocyclobutenone (Fig. 1, Eq. 3, 7) (4). The direct adducts of this [4+2] reaction (compare 8) are readily converted to norcarane carboxylic acids (9) through exposure to hydroxide base. The research described herein was initially focused on efforts to add carbon-based nucleophiles to DA cycloadducts of the type 8. It might well have been expected that such reactions would give rise to products such as 10, wherein a ketone is appended to the junction of the norcarane system (Fig. 1, Eq. 4). Results and DiscussionWith a view toward accomplishing the transformation envisioned in Fig. 1, Eq. 4, compounds of the type 8 were exposed to methyllithium as described in Fig. 2. Interestingly, exposure of substrate 8a to the conditions shown led to an 81% yield of the angularly methylated product 11a, apparently unaccompanied by any part of the corresponding trans-fused diastereomer (Fig. 2, entry 1). Reactions conducted with related DA adducts 8b and 8c resulted in quite similar outcomes (Fig. 2, entries 2 and 3). Although we were confident that the products obtained were cisfused (Fig. 2, 11a-c), it was the synthesis of the rigorously assignable trans-fused product (vide infra) and its nonidentity with 11a that served to allow for sound assignment of the cisring fusion.An obvious mechanistic proposal to account for the formation of this structure envisions lithium-halogen exchange (5-8) leading to 12a and methyl bromide (Fig. 3). This step is followed by angular methylation (9-11) of 12a. It would not be surprising for such a reaction to have a very high preference for producing cis fusion. Clearly, a great deal of ring strain would be introduced in any transition state en route to trans-fused products.Whereas the enolate alkylation proposal is presumptive, several alternate formulations merited consideration. In principle, one can envision the possibility that lithium enolate 12a is not actually produced (perhaps due to ring strain). Rather, 11 (Fig. 3) arises from the merger of otherwise high-energy species en route to 12a and 12b. For instance, "radicaloid" (5) character could be generated at both the bridgehead ...

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“…The 6-hepten-2-yl radical cyclizes with a preference for the cis-stereochemistry while the corresponding organolithium gives predominantly the trans-isomer. [15][16][17][18] Cohen et al used such cis-/trans-ratios of cyclization products to show that unsaturated alkylzinc iodides cyclize by a radical rather than a polar mechanism. They found that probably all of the organozinc cyclizations are radical chain reactions initiated by traces of oxygen.…”

Section: Methodsmentioning

confidence: 99%

Clear-cut difference in the rearrangement of 1-bromo-2-(2-phenyl-3-butenyl)benzene under anionic or radical conditions

Reynaud¹,

Hazimeh²,

Mattalia³

et al. 2011

Arkivoc

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The o-(3-butenyl)phenyl system bearing a phenyl group on the 2-position of the side chain was studied as a potential mechanistic probe for distinguishing between radical and carbanion intermediates. The Bu3SnH reduction of 1-bromo-2-(2-phenyl-3-butenyl)benzene, 4, yields mainly the 1,5-cyclization product, 6, with a preference for the trans-isomer. Treatment of 4 with Mg or t-BuLi leads to double-bond isomerization and yields (E)-1,2-diphenyl-2-butene, 8, along with 3,4-diphenyl-1-butene, 5.

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The mechanism of the lithium - halogen Interchange reaction : a review of the literature

Cited by 231 publications

References 137 publications

Synthesis and characterization of macrocyclic vinyl aromatic polymers

Synthesis and characterization of macrocyclic vinyl aromatic polymers

Stereospecific cis- and trans -ring fusions arising from common intermediates

Clear-cut difference in the rearrangement of 1-bromo-2-(2-phenyl-3-butenyl)benzene under anionic or radical conditions

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