Acid-catalyzed hydration of di-tert-butylketene

Kabir, Shaikh H.; Seikaly, Hani R.; Tidwell, Thomas T.

doi:10.1021/ja00498a059

Cited by 27 publications

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“…The 13 C and 29 Si NMR chemical shifts of the silylated diphenylketene 5 in solution are summarized in Table 2. The silylation of diphenylketene thus afforded a single isomer, C ␤ -silylated diphenylketene 5, as indicated by 1 H, 13 C, and 29 Si NMR spectroscopy. The isomer is stable at temperatures up to Ϫ20°C.…”

Section: Resultsmentioning

confidence: 96%

“…This value also suggests some transfer of positive charge to silicon through hyperconjugation. The calculated 13 C NMR chemical shifts of CO ϩ and C ␤ carbons of 3b are 174.3 and 34.2 ppm, respectively. These are substantially more shielded by 12.8 and 25.1 ppm, respectively, than the experimentally observed values of 187.1 and 59.3 ppm in 5.…”

Section: Resultsmentioning

confidence: 97%

“…However, in the case of ketenes with both substituents bulkier than H, the O-silylated isomers were found to be more stable: 4e is more stable than 3e by 0.3 kcal͞mol, and 4f is more stable than 3f by 1.9 kcal͞mol (Table 1). We have also computed 13 C and 29 Si NMR chemical shifts of 3b and 4b using the IGLO method (26) at the IIЈ level using B3LYP͞6-311ϩG* geometries ( Table 2). Huzinaga (27) Gaussian lobes were used as follows.…”

Section: Resultsmentioning

confidence: 99%

“…The isomer is stable at temperatures up to Ϫ20°C. The selected 13 C NMR data are compiled in Table 2. The peak at ␦ 13 C 187.1 ppm is assigned to the CO ϩ carbon.…”

Section: Resultsmentioning

confidence: 99%

“…The peak at ␦ 13 C 187.1 ppm is assigned to the CO ϩ carbon. Comparison of the 13 C NMR data for silylated diphenylketene 5 and protonated diphenylketene 2b is informative concerning the charge distribution of the acylium ions. The reported ␦ 13 C of the CO ϩ in 2b is 154.7 ppm, consistent with the typical acylium ion resonance structures (28).…”

Section: Resultsmentioning

confidence: 99%

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The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

Prakash

Bae²,

Rasul³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Electrophilic triethylsilylation of diphenylketene leads to exclusive C-silylation giving the diphenyl(triethylsilyl)acetyl cation in the solution phase even though density functional theory calculations at the B3LYP͞6-311؉G* level indicate that the O-silylation of diphenylketene is preferred over C-silylation by 5.4 kcal͞mol in the gas phase. On the other hand, in the case of the parent ketene, similar density functional theory calculations show that C-silylation is preferred over O-silylation by 8.2 kcal͞mol.K etenes are unusual alkenes as well as carbonyl compounds that are reactive toward both electrophiles and nucleophiles. From 13 C NMR chemical shift studies it has been shown that ketenes are highly polarized molecules with the C ␤ and oxygen atoms bearing a substantial negative charge and C ␣ bearing the positive charge (ref. 1; for a review, see ref.2). Electrophiles attack at C ␤ or oxygen centers from above or below the plane of the ketenes, and nucleophiles attack at C ␣ in plane. Protonation of ketenes has been the subject of numerous experimental and theoretical studies. Theoretical studies (3)(4)(5)(6)(7)(8) show that the protonation at C ␤ of ketene 1a (to form acylium ion 2a in Eq. 1) is more favorable than protonation at oxygen (to form Oprotonated ion) by 43 kcal͞mol. In solution, the site of proton addition to ketenes has been mostly determined from kinetic studies of acid-catalyzed hydration (9-13). We have previously shown that protonation of diphenylketene and of di-tertbutylketene in Magic Acid solution at low temperature resulted in the formation of corresponding acylium ions 2b and 2c (Eq. 1), as indicated by the 13 C NMR signals for CO ϩ at ␦ 13 C 154.7 and 154.1, respectively (14).Long lived trialkylsilyl cations are still elusive in the condensed phase due to their kinetic instability. The in situ generation of trialkylsilyl cations in solution, by hydride transfer͞abstraction from organohydrosilanes by the triphenylmethyl (trityl) cation (so-called ''Corey hydride transfer'') (15), has been adopted for the preparation of a number of silylated onium ions (16-21). However, electrophilic silylation of ketenes has not yet been reported. Thus far, silylation of ketenes employing silicon compounds has been known to produce only silyl enol ethers, formed by nucleophilic addition of a leaving group, such as CN Ϫ or N 3 Ϫ , at C ␣ followed by O-silylation (22, 23). Herein, we report a theoretical and experimental study of electrophilic silylation of ketenes in solution. In principle, the incipient silyl cation may react with the C ␤ of ketene to give ␤-silylacylium ion or with oxygen to give silylcarboxonium ion due to strong Si-O bond formation (Eq. 2). Experimental MethodsThe preparation of ␤-silyl carbenium ion 5 was as follows. Diphenylketene (0.13 mmol) and triethylsilane (25 mg, 0.22 mmol) in dry CD 2 Cl 2 (0.25 ml) were loaded into a dry, 5-mm NMR tube in a glove box under an argon atmosphere. The NMR tube was taken out of the glove box and then cooled by using dry ice͞acetone to Ϫ78°...

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Section: Resultsmentioning

confidence: 96%

Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

“…The isomer is stable at temperatures up to Ϫ20°C. The selected 13 C NMR data are compiled in Table 2. The peak at ␦ 13 C 187.1 ppm is assigned to the CO ϩ carbon.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 3 more Smart Citations

The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

Prakash

Bae²,

Rasul³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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ChemInform Abstract: ACID‐CATALYZED HYDRATION OF DI‐TERT‐BUTYLKETENE

Kabir¹,

Seikaly²,

Tidwell³

1979

Chemischer Informationsdienst

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Acylation Mechanisms of DMSO/[D₆]DMSO with Di‐tert‐butylketene and Its Congeners

Knorr

2011

Eur J Org Chem

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Dimethyl sulfoxide (DMSO) and tBu 2 C=C=O in diglyme require heating to about 150°C to furnish the Pummerer-type product tBu 2 CHCO 2 CH 2 SCH 3 through a novel mechanistic variant. The "ester enolate" tBu 2 C=C(O -)-O-S + (CH 3 ) 2 arising through the reversible addition of DMSO (step 1) to C-1 of tBu 2 C=C=O must be trapped through protonation (step 2) at C-2 by a carboxylic acid catalyst to form tBu 2 CH-C(=O)-O-S + (CH 3 ) 2 so that the reaction can proceed. The ensuing cleavage (step 3) of the O-S bond and one of the C-H bonds in the -S(CH 3 ) 2 group (E2 elimination, no ylide intermediate) results in the formation of tBu 2 CHCO 2 -and H 3 CS-CH 2 + , whose combination (step 4) generates the final product. With a mixture of DMSO and [D 6 ]DMSO competing for tBu 2 C=C=O in diglyme, the small value of the kinetic H/D isotope effect (KIE) k H /k D = 1.26 at 150°C indicates that the cleavage of the C-H/C-D bonds (step 3) does not occur in the transition state with the highest free enthalpy. Therefore, the practically isotope-independent steps 1 and 2 determine

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Acid-catalyzed hydration of di-tert-butylketene

Abstract: 2) Argoudelis, A. D.; Herr, R. R. Antimicrob. Agents Chemother. 1962, 780-786. (3) Higashide, E.; Hasegawa, T.; Shibata, M.; Mizuno, K.; Akaike, H. Takeda

Cited by 27 publications

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The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

ChemInform Abstract: ACID‐CATALYZED HYDRATION OF DI‐TERT‐BUTYLKETENE

Acylation Mechanisms of DMSO/[D₆]DMSO with Di‐tert‐butylketene and Its Congeners

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Acid-catalyzed hydration of di-tert-butylketene

Abstract: 2) Argoudelis, A. D.; Herr, R. R. Antimicrob. Agents Chemother. 1962, 780-786. (3) Higashide, E.; Hasegawa, T.; Shibata, M.; Mizuno, K.; Akaike, H. Takeda

Cited by 27 publications

References 0 publications

The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

The question of C- vs. O-silylation of ketenes: Electrophilic triethylsilylation of diphenylketene

ChemInform Abstract: ACID‐CATALYZED HYDRATION OF DI‐TERT‐BUTYLKETENE

Acylation Mechanisms of DMSO/[D6]DMSO with Di‐tert‐butylketene and Its Congeners

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Acylation Mechanisms of DMSO/[D₆]DMSO with Di‐tert‐butylketene and Its Congeners