Triflic Acid Promoted Direct α-Alkylation of Unactivated Ketones Using Benzylic Alcohols via in Situ Formed Acetals

Koppolu, Srinivasa Rao; Naveen, Naganaboina; Balamurugan, Rengarajan

doi:10.1021/jo500759a

Cited by 39 publications

(19 citation statements)

References 84 publications

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“…For instance, in the addition of active aldehyde and diarylmethanols, 20 mol % TfOH was used to activate bis(4‐chlorophenyl)methanol to obtain a moderate ∼53 % yield of the α‐alkylation product; for poorly active ketones an increased amount of TfOH had to be used (1 equiv.) along with trimethyl orthoformate . It is believed that TfOH promoted the in situ generation of dimethyl acetal to facilitate the smooth generation of methyl vinyl ether.…”

Section: Introductionmentioning

confidence: 99%

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

et al. 2016

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A “release and catch” method was developed by utilising the scavenging effect of a fluorous zwitterion on a homogeneous triflic acid (TfOH) catalyst in Michael addition and Rupe rearrangement. Both TfOH and the zwitterion were recycled with >90 % recovery using toluene. The zwitterions were designed by functionalising imidazole/pyridine with the perfluoroalkylsulfonylimide group. The “caught” TfOH was delivered to ethyl acetate and re‐used. The smooth delivery was primarily because of the fluorous tail of the zwitterion, the hydrophobicity of which probably weakened the ability of the zwitterion to form H bonds, so that retro‐ion‐exchange occurred towards the formation of the acid and zwitterion. The method was universal for other strong Brønsted acids such as H2SO4 and p‐MeC6H4SO3H. The method combined the significant advantages of homogeneous catalysis and heterogeneous isolation. Based on the H0 acidity function and the 31P NMR chemical shift of Et3P=O adducts, it is reasonable to deduce that the decrease of the acid strength of the formed composites of Brønsted acids and the zwitterion drove the scavenging effect.

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Section: Introductionmentioning

confidence: 99%

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

et al. 2016

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“…In our efforts to develop organic transformations using in‐situ‐formed acetals,6 we found that alkyl ketones generate enol ethers via in‐situ‐formed acetals under Lewis/Brønsted acidic conditions in the presence of trimethyl orthoformate. It was demonstrated that the formed enol ether could be alkylated directly with various alcohols using either triflic acid (TfOH)6d or AgSbF 6 6e. Recently, we reported an acetal‐assisted intermolecular alkyne–carbonyl metathesis and intramolecular annulation between o ‐alkynylbenzaldehydes and alkynes in the presence of trimethyl orthoformate and catalytic Brønsted acid for the synthesis of substituted benzo[ a ]fluorene derivatives 6c.…”

Section: Introductionmentioning

confidence: 99%

A Cascade Approach to Naphthalene Derivatives from o‐Alkynylbenzaldehydes and Enolizable Ketones via in‐situ‐Formed Acetals

Manojveer

Balamurugan

2015

Eur J Org Chem

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Using the in‐situ‐formed acetal strategy, a facile approach has been developed to synthesize naphthalene derivatives from o‐alkynylbenzaldehydes and enolizable ketones. In situ acetal formation assists the condensation between o‐alkynylbenzaldehydes and enolizable ketones to give chalcone derivatives under Brønsted acidic conditions. In situ acetal formation facilitates the reaction by increasing the electrophilicity of the carbonyl carbon of the o‐alkynylaldehyde through oxonium ion formation, and also by enhancing the nucleophilicity of the α carbon of the ketone through the formation of an enol ether. The formed chalcones undergo trans to cis isomerization to effect alkyne–carbonyl metathesis to give naphthalene derivatives.

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“…This can easily be understood from the limited substrate scope of diarylmethanols in the alkylation reactions with ketones 3e,4e. In our research endeavours to utilize in situ formed acetals6 we have found that a stoichiometric amount of TfOH is able to promote the direct α‐alkylation of different ketones with a wide range of benzylic alcohols at room temperature 6c. The success of the reaction is due to the formation of methyl vinyl ether from the ketone via an in situ generated acetal formed by the reaction of trimethyl orthoformate with the ketone in the presence of triflic acid 7.…”

Section: Introductionmentioning

confidence: 99%

Silver Hexafluoroantimonate‐Catalyzed Direct α‐Alkylation of Unactivated Ketones

2015

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A practically simple and direct a-alkylation of unactivated ketones using benzylic alcohols has been achieved. The in situ formed acetals are the key for the success of the reaction. The catalyst, silver hexafluoroantimonate(V) (AgSbF 6 ) provides double activation by converting the ketone into an enol ether via acetal and generation of carbocationic center at the benzylic position of the benzylic alcohol. The alcohols include benzylic propargyl alcohols, cinnamyl alcohols, and diarylmethanols.

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Triflic Acid Promoted Direct α-Alkylation of Unactivated Ketones Using Benzylic Alcohols via in Situ Formed Acetals

Cited by 39 publications

References 84 publications

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

“Release and Catch” Effect of Perfluoroalkylsulfonylimide‐Functionalized Imidazole/Pyridine on Brønsted Acids in Organic Systems

A Cascade Approach to Naphthalene Derivatives from o‐Alkynylbenzaldehydes and Enolizable Ketones via in‐situ‐Formed Acetals

Silver Hexafluoroantimonate‐Catalyzed Direct α‐Alkylation of Unactivated Ketones

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