Ion Cyclotron Resonance Studies of Alkylsilyl Ions. II. The Reactions of Ketones, Carboxylic Acids and Esters with the Trimethylsilyl Cation

1979 ◽  
Vol 32 (6) ◽  
pp. 1389 ◽  
Author(s):  
IA Blair ◽  
JH Bowie
Keyword(s):  
Carboxylic Acid ◽  
Transition State ◽  
Lewis Acid ◽  
Cyclotron Resonance ◽  
Nucleophilic Attack ◽  
Ion Cyclotron Resonance ◽  
Deuterium Isotope Effect ◽  
Trimethylsilyl Cation ◽  
A Minor ◽  
Membered Transition State

Nucleophilic attack of a ketone, carboxylic acid or ester at the electrophilic centre of the trimethylsilyl cation (Me,Si+) produces a 1:1 adduct. This adduct does not decompose in the case of ketones. Acid adducts decompose primarily by loss of methane, but a minor pathway exists which involves elimination of a ketene. Ester adducts fragment primarily by this latter process through a four-membered transition state. The transfer of hydrogen was shown to arise solely from the acyl group and was shown to proceed with a small deuterium isotope effect. Further decomposition of the resulting ion by loss of methane provides unequivocal proof that esters react predominantly through the alkyl oxygen with the Lewis acid Me3Si+.

Ion-Cyclotron Resonance Studies of Alkylsilyl Ions. I. The Reactions Between Alcohols and the Trimethylsilyl Cation

1979 ◽  
Vol 32 (1) ◽  
pp. 59 ◽  
Author(s):  
IA Blair ◽  
G Phillipou ◽  
JH Bowie
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Cyclotron Resonance ◽  
Nucleophilic Attack ◽  
Ion Cyclotron Resonance ◽  
Trimethylsilyl Cation ◽  
Ion Cyclotron ◽  
Decomposition Pathway ◽  
Membered Transition State

Nucleophilic attack of an alcohol (ROH) at the electrophilic silicon centre of the trimethylsilyl cation (Me3Si+) produces the 1 : 1 adduct Me3-O+(H)R(1). The adduct may fragment by loss of methane to yield Me2Si+-O-R; and this elimination is most pronounced when R = Me. When R ≥ C2H5, the major decomposition pathway of (1) involves elimination of the alkene [R-H] to produce Me3Si-O+H2, which may undergo further reaction with the neutral alcohol to reform (1). The proton transfer which accompanies the elimination of [R- H] from (1) originates predominantly from C2 of the alcohol; this suggests the intermediacy of a four-membered transition state in this reaction.

The Reactions of Alkoxide-Alkanol Negative Ions with Ketene. An ab initio and Ion Cyclotron Resonance Study

1985 ◽  
Vol 38 (3) ◽  
pp. 355 ◽  
Author(s):  
RN Hayes ◽  
JC Sheldon ◽  
JH Bowie
Keyword(s):  
Ab Initio ◽  
Cyclotron Resonance ◽  
Negative Ions ◽  
Ion Cyclotron Resonance ◽  
Reaction Sequence ◽  
Major Pathway ◽  
Stable Species ◽  
Product Ions ◽  
A Minor ◽  
Competing Reactions

Alkanol-alkoxide negative ions [RO----HOR] react with ketene to form stable species H-C≡C-O----HOR. The initial intermediate in the reaction sequence is produced by the formation of a hydrogen bond between the negatively charged oxygen of [RO----HOR] and a hydrogen of ketene. This intermediate decomposes by competing reactions, viz. ( i ) a minor pathway involving direct elimination of ROH, and (ii) a major pathway involving a rearrangement sequence. Intermediates and product ions have been defined by using ab initio calculations at the 4-31G level. The differences between the reactions of [RO----HOR]/ketene and [RO---- HOR]/acetaldehyde systems are discussed.

scholarly journals Nickel-Catalysed Allylboration of Aldehydes

Synthesis ◽  
2020 ◽  
Vol 52 (13) ◽  
pp. 1903-1914 ◽  
Author(s):  
Benjamin M. Partridge ◽  
Francesca M. Dennis ◽  
Craig C. Robertson
Keyword(s):  
Transition State ◽  
Nickel Catalyst ◽  
Lewis Acid ◽  
Homoallylic Alcohols ◽  
Membered Transition State

A nickel catalyst for the allylboration of aldehydes is reported, facilitating the preparation of homoallylic alcohols in high diastereoselectivity. The observed diastereoselectivities and NMR experiments suggest that allylation occurs through a well-defined six-membered transition state, with nickel acting as a Lewis acid.

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