Novel hypervalent (10-I-2) iodine structures

Farnham, William B.; Calabrese, Joseph C.

doi:10.1021/ja00269a055

Cited by 81 publications

(44 citation statements)

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“…In view of the precedent set by Calabrese [9] and Reich [8] we feel confident that the intermediate observed is the iodine ± ate complex 5.…”

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confidence: 64%

“…[8] In parallel, Calabrese successfully crystallized an ate complex (1, R 1 R 2 C 6 F 5 ) in which the lithium cation is shielded by two TMEDA ligands. [9] We report here the direct observation of an iodine ± ate complex (5) in the iodine ± magnesium exchange reaction [10] of 1,1-diiodoalkanes 2 (Scheme 1). Treatment of 2 with isopropylmagnesium bromide for two hours at À 78 8C in THF provided the carbenoid 3 quantitatively, as evidenced by the formation the iodoalkane 6 upon quenching with CH 3 OH.…”

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confidence: 99%

“…Surprisingly, there were no studies till now in which the number of single bonds in supramolecular complexes was systematically varied. We chose a series of a,w-diamides as hydrogen-bond donors [9] and a,w-dicarboxylates as acceptors. [10] The tetrabutylammonium salts of the latter are soluble in chloroform.…”

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confidence: 99%

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α-Iodoalkyl-Iodine-Ate Complexes as Observable Intermediates in the Iodine- Magnesium Exchange Reaction

Schulze

Brönstrup

Böhm

et al. 1998

Angewandte Chemie International Edition

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“…In view of the precedent set by Calabrese [9] and Reich [8] we feel confident that the intermediate observed is the iodine ± ate complex 5.…”

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confidence: 64%

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confidence: 99%

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α-Iodoalkyl-Iodine-Ate Complexes as Observable Intermediates in the Iodine- Magnesium Exchange Reaction

Schulze

Brönstrup

Böhm

et al. 1998

Angewandte Chemie International Edition

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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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“…8,a). 9 ) The small shoulder on the side of the peak at 445 ppm in the spectra at À 1308 to À 1498 is the protonated compound. .…”

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The Role of Ate Complexes in the Lithium-Sulfur, Lithium-Selenium and Lithium-Tellurium Exchange Reactions

Reich

Gudmundsson

Green

et al. 2002

HCA

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This paper is dedicated to Professor Dieter Seebach in honor of his 65th birthday Hypervalent ate complexes are presumptive intermediates in the metal-halogen, metal-tellurium, and related exchange reactions. The effect of o,o'-biphenyldiyl vs. diphenyl substitution on formation of tellurium ate complexes was studied by a kinetic technique and by NMR spectroscopy. Only a modest increase in the association constant (K ate ) was measured. When Li/M exchanges of o,o'-biphenyldiyl sulfides and selenides were made intramolecular by means of a m-terphenyl framework (12-S, 12-Se, 21), enormous increases (> 10 9 ) in the rate of Li/S and Li/Se exchange were observed compared to acyclic models. Apparently, these systems are ideally preorganized to favor the T-shaped geometry of the hypervalent intermediates. For the selenium systems, ate complex intermediates (20-Se, 26) were detected spectroscopically in THF-or THF/HMPA-containing solutions. A DNMR study showed that Li/Se exchange was substantially faster than exchange of the lithium reagents with the ate complex. Therefore, these ate complexes are not on the actual Li/Se exchange pathway.Introduction. ± The lithium-metalloid exchange reaction is the mildest and most general procedure for the preparation of organolithium reagents. The lithium-bromine [1] [2a] and lithium-iodine exchanges have been the most popular, but the reaction applies to many of the main-group third-, fourth-, and fifth-row elements. Tin [3a] [4], selenium (first studied by Seebach and Peleties [3b], and tellurium [3c] have been used extensively. The reaction fails with second-row CÀM bonds like those of chlorides, sulfides, and phosphines, except in exceptional circumstances, e.g., when there are no protons that can be metallated, when an unusually stable carbanion is being prepared, or when a strained ring is being cleaved [5] [6].Hypervalent ate complexes such as 1 ± 3 have been spectroscopically characterized and are likely intermediates in the degenerate phenyl-phenyl Li/I [7a] [7b] [8] [9], Li/Te [7b] [7c] [10a], and Li/Sn [7d] [11] [12] exchange reactions. Ate complexes of third-and even second-row metalloids Se, P, and Si can be detected in favorable structures, e.g., when the aryl groups are heavily substituted with electronegative halogen atoms (4, see [10b]) or when o,o'-biphenyldiyl ligands are present (5, see [13] and 6, see [14a]).

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Novel hypervalent (10-I-2) iodine structures

Cited by 81 publications

References 1 publication

α-Iodoalkyl-Iodine-Ate Complexes as Observable Intermediates in the Iodine- Magnesium Exchange Reaction

α-Iodoalkyl-Iodine-Ate Complexes as Observable Intermediates in the Iodine- Magnesium Exchange Reaction

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

The Role of Ate Complexes in the Lithium-Sulfur, Lithium-Selenium and Lithium-Tellurium Exchange Reactions

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