2010
DOI: 10.1021/ol100450s
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Unusual Carbon−Carbon Bond Formations between Allylboronates and Acetals or Ketals Catalyzed by a Peculiar Indium(I) Lewis Acid

Abstract: In(I)OTf has been uncovered as an effective Lewis acid catalyst for unprecedented nucleophilic substitution of acetals or ketals with allylboronates. A transmetalative S(N)1 mechanism is proposed in which a single In(I) center acts as a dual catalyst to activate both reagents sequentially. Contrary to the classic gamma-selectivity of allylsilanes (Hosomi-Sakurai reaction), this In(I)-catalyzed borono variant displays distinct alpha-selectivity. Substrate scope and functional group tolerance proved to be excell… Show more

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Cited by 38 publications
(47 citation statements)
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“…[7] We have proposed a transmetalative S N 1 mechanism, in which indium(I) plays a dual role, as shown in Figure 1. [6] In the case of allyl borane 2 b, however, we cannot rule out a nontransmetalative pathway, which involves the direct reaction of the more reactive boron-ate complex D with electrophile A. The in situ-formed InOMe then triggers B-to-In transmetalation with borane 2 b (or boronate 2 a) to generate the nucleophilic allyl indium(I) species (B), which subsequently reacts with electrophile A to give the desired allylated product 3.…”
Section: Resultsmentioning
confidence: 99%
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“…[7] We have proposed a transmetalative S N 1 mechanism, in which indium(I) plays a dual role, as shown in Figure 1. [6] In the case of allyl borane 2 b, however, we cannot rule out a nontransmetalative pathway, which involves the direct reaction of the more reactive boron-ate complex D with electrophile A. The in situ-formed InOMe then triggers B-to-In transmetalation with borane 2 b (or boronate 2 a) to generate the nucleophilic allyl indium(I) species (B), which subsequently reacts with electrophile A to give the desired allylated product 3.…”
Section: Resultsmentioning
confidence: 99%
“…This rare a-selectivity with 2 c is a strong indicator for catalytic B-to-In transmetalation prior to CÀC bond formation. [6] Finally, without 4 a, the reaction with allenyl boronate 2 e hardly proceeded (Table 6, entry 5). The low reactivity of these boronates is consistent with our previous work, and may be explained by a particularly slow transmetalation owing to steric congestion at the g-position.…”
Section: Resultsmentioning
confidence: 99%
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“…24 Furthermore, recent reports have shown that such reactions can be rendered enantioselective. In our own efforts, we recently reported a cross-coupling strategy for the preparation of dialkyl ethers by the BF 3 •OEt 2 -promoted reaction of potassium organotrifluoroborates and O -MOM acetals (Scheme 1).…”
Section: Introductionmentioning
confidence: 99%
“…R 1 = alkyl, aryl, heteroaryl (ees: 72-97%)3.3.2 Indium(I) TriflateBorono Variant of Hosomi-Sakurai Reaction with Acetals or Ketals: Synthesis of Homoallyl Ethers The In(OTf)-catalyzed reaction of acetals or ketals with allylboronic acid pinacol esters allows access to various homoallyl ethers(71) 99. Deuterium-labeling experiments support a transmetalative S N 1 mechanism involving the reaction of an In(I)-allyl species with an oxonium triflate intermediate as a key step for product formation.…”
mentioning
confidence: 99%