Nucleophilic Reactivities of Ketene Acetals

Abstract

Keywords: Carbocations / CϪC coupling / Kinetics / Linear free energy relationship / Substituent effectsThe kinetics of the reactions of ketene acetals with benzhydrylium ions have been followed photometrically. The reactions proceed with rate-determining C−C bond formation that is considerably faster than expected for outer-sphere electron transfer processes. Structure−reactivity relationships are discussed. The excellent correlations between the observed second-order rate constants (log k 2 ) and the previ-

Quantification of the β‐Stabilizing Effect of the Dicarbonyl(η5‐cyclopentadienyl)iron Group

“…The reactions of benzhydrylium tetrafluoroborates with silylated enol ethers or silylated −ketene acetals× have been demonstrated to proceed with rate-determining CÀC bond formation, followed by fast desilylation [23] [30]. Hence, a similar course can be expected for the reactions of 9 ¥ BF 4 with the nucleophiles 10b ± e, as shown in Scheme 7.…”

“…In both series, the allyl compounds (Fig. 2, left row) and their 2-methyl analogues (right row), the b-activating effect of the Fp group exceeds that of the corresponding Sn compounds considerably, and is responsible for the fact that compounds 1a,b rank among the strongest neutral p-nucleophiles, comparable to silylated −ketene acetals× [1] [23], only exceeded by enamines [24].…”

Bis(trimethylsilyl)ketene Acetals as C,O‐Dinucleophiles: One‐Pot Formation of Polycyclic γ‐ and δ‐Lactones from Pyridines and Pyrazines

“…The transformation of these nitrogen-containing acids and, more interestingly, of their trimethylsilyl ester precursors into lactones of various sizes by an intramolecular one-pot approach has been outlined. The scope and the limitations of these reactions were established, confirming the high nucleophilicity of ketene acetals [68,69] and the great potential properties of a special class of these derivatives, bis(trimethylsilyl)ketene acetals, as 1,3-carbon,oxygen dinucleophiles.…”

Correlations Between Nucleophilicities and Selectivities in the Substitutions of Tetrahydropyran Acetals

“…41,42 The nucleophilicity values ( N ), derived by Mayr and co-workers, correlate logarithmically with rates of reactions with carbocationic electrophiles. 41,43 The nucleophiles selected for this study represent a range in reactivity that spans over eight orders of magnitude, 41 from the least reactive, allyltrimethylsilane 1 ( N = 1.8), to the most reactive, alkylsilyl ketene acetal 10 ( N = 10.2).…”