Preparation of 1-aryl-2-siloxyalkynes from silylated .alpha.-diazocarbonyl compounds

Maas, Gerhard; Brueckmann, R.

doi:10.1021/jo00215a049

Cited by 59 publications

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“…The silylated adiazo ketones 6 are obtained under mild conditions in satisfactory to good yields by an electrophilic diazoalkane substitution at primary a-diazo ketones 4 with highly electrophilic trialkylsilyl triflates 5 as silylating reagents. This method had been used before for C-silylation of diazomethane*), ethyl diazoacetate**", (diazomethy1)phosphoryl compounds"', and diazo ketones ArCOCHN;'.…”

Section: Synthesis Of U-diazo-a-(trialkylsilyl)alkanonesmentioning

confidence: 99%

Thermal Decomposition of α‐Diazo‐α‐(trialkylsilyl)alkanones – Intramolecular C/H Insertion of Siloxyalkylidenecarbene Intermediates

Brückmann

Maas

1987

Chem. Ber.

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a-Diazo-a-(trialkylsilyl)alkanones 6 have been prepared by silylation of primary a-diazo ketones 4 with trialkylsilyl triflates 5. Diazo compounds 6 are decomposed in boiling benzene to give l-oxa-2-sila-4-cyclopentenes 7 and 9. Evidence is presented that this transformation proceeds via alkylidenecarbenes 17 which undergo 1,5-cyelization by carbcne insertion into a Sic-H bond.The synthetic potential of a-diazocarbonyl compounds rests to a marked extent on their lability towards UV light, elevated temperature, and certain transition metals, which makes them a convenient and easily accessiblc source of carbenes or carbenoids".However, there is an obvious lack of information concerning the chemistry of a-(silyldiazomethyl)arbonyl compounds. Silylated diazo esters (la) and some r*-(silyldiazomethyl) ketones of type 1 b represent the exceptions; the prime interest in their chemistry was directed towards the eventual formation of silenes from silylated ketocarbenes derived from 1 a, b2'. As the sole "simple" silylated diazo ketone, 1 -diazo-1 -(triethylsilyl)-2-propanone has been prepared, and its thermal decomposition in the presence of copper has been studied 31. Recently, we have reported that (aroyldiazomethy1)silanes 1 c easily sulTer thermal dediazoniation with transformation into siloxyalkynes 34! Siloxyalkylidene carbenes 2 are considered the immediate precursors of the alkynes. The 1,2-aryl migration which brings about the transformation 2+3 has precedent in earlier work of Stangs', Gilbert ", and their coworkers who have shown that in alkylidenecarbenes [Ar(R)C=C:, R = alkyl, aryl] the aryl shift is usually faster than any other intra-or intermolecular trapping reaction of this carbene. On the other hand, an alkyl group is not prone to a facile 1,2-migration to the vinylidene carbon, as several successful intermolecular trapping rcactions of alkylidenecarbenes bearing Balky1 groups indicate"". We have therefore synthesized (alkanoyldiazomcthyl)silanes 6 which, by thermal decomposition, should give access to alkylidenecarbenes analogous to 2. Since B aryl groups were no longer present. the way seemed to be paved for other intra-or intermolecular reactions of these reactive intermediates. R,Si-C-CO,R Me3SiMe2C-CR III1 Synthesis of u-Diazo-a-(trialkylsilyl)alkanones 6The silylated adiazo ketones 6 are obtained under mild conditions in satisfactory to good yields by an electrophilic diazoalkane substitution at primary a-diazo ketones 4 with highly electrophilic trialkylsilyl triflates 5 as silylating reagents. This method had been used before for C-silylation of diazomethane*), ethyl diazoacetate**", (diazomethy1)phosphoryl compounds"', and diazo ketones ArCOCHN;'. Other approaches to silylated a-diazo ketones are given by acylation of lithio(pentamethyldisilanyl)diazomethane'l) and by the reaction between bis(triethylsily1)mercury and mercury-bis(diazo ketones), Hg[C(N2)COR];'; the latter reaction made diazo ketone 6aA available3'. As in the case of (aroyldiazomethy1)silanes 1 c4), the high lability of the C(N2...

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Section: Synthesis Of U-diazo-a-(trialkylsilyl)alkanonesmentioning

confidence: 99%

Thermal Decomposition of α‐Diazo‐α‐(trialkylsilyl)alkanones – Intramolecular C/H Insertion of Siloxyalkylidenecarbene Intermediates

Brückmann

Maas

1987

Chem. Ber.

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“…[8] To our surprise, the aryl trialkylsilyl ketenes 3a-d rather than silyldiazo ketones 2 were obtained when the reactions were carried out in dichloromethane or chloroform solution (Ͼ95 % conversion according to 1 H NMR spectroscopy, see for example the spectrum of crude 3c in the Supporting Information; 60-70 % yield after kugelrohr distillation). In these solvents, ammonium triflate 4 is completely soluble, suggesting that it catalyzes the conversion of first-formed diazo ketones 2 into silyl ketenes 3.…”

Section: Resultsmentioning

confidence: 99%

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) practical method to prepare α-silyl α-diazo ketones. [4,8,9] Typically, diethyl ethyl ether is used as the reaction medium, from which most (but not all) of the formed trialkylammonium triflate precipitates as the reaction proceeds. In order to avoid protonation/desilylation of the product by the acidic ammonium salt, Danheiser et al have used the less polar reaction medium diethyl ether/hexane (1:1), in which the ammonium salt is less soluble, and in fact obtained the silyldiazo ketones in higher yields.…”

Section: Resultsmentioning

confidence: 99%

“…[10] The silylation of diazomethyl ketones 1a-c with trimethylsilyl triflate or triethylsilyl triflate and diisopropylethylamine in ether or diethyl ether/pentane mixtures provided the corresponding α-silyl α-diazo ketones 2a-e (Scheme 1). The synthesis of 2b and 2d by this method has been described before, [4,8] but in the present study we prepared only concentrated solutions of 2a-e that were suitable for further transformations (see below). It should be recalled that no α-Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

“…The alternative pathway, N 2 extrusion from 2Ј and [2+1] cycloaddition of the resulting vinylidene, is disfavored, because these β-arylalkylidene carbenes would undergo rapid 1,2-aryl shift to form silyloxyalkynes. [8] Scheme 6. Proposed mechanism for the formation of allenes 5.…”

Section: Resultsmentioning

confidence: 99%

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Aryl Trialkylsilyl Ketenes: Acid‐Catalyzed Synthesis from 1‐Aryl‐2‐diazo‐2‐trialkylsilylethanones and Their Conversion into 3‐Silyl‐1‐silyloxyallenes

2008

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Aryl‐substituted α‐silyl α‐diazo ketones are readily transformed into aryl silyl ketenes in the presence of a catalytic amount of triflic acid. Thus, a convenient method to prepare these silyl ketenes becomes available, which combines two steps, silylation of an aryl diazomethyl ketone and acid‐induced Wolff rearrangement of the formed α‐silyl α‐diazo ketone, in a one‐pot procedure. It appears that the trialkylammonium salt, which is formed in the silylation step, can also catalyze the Wolff rearrangement, but distinctly more slowly than the proton acid. The silyl ketenes react smoothly with α‐silyl α‐diazo ketones to form 3‐silyl‐1‐silyloxyallenes in fairly good yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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Triethylsilyl Trifluoromethanesulfonate

Turos¹

2001

Encyclopedia of Reagents for Organic Synthesis

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Preparation of 1-aryl-2-siloxyalkynes from silylated .alpha.-diazocarbonyl compounds

Cited by 59 publications

References 0 publications

Thermal Decomposition of α‐Diazo‐α‐(trialkylsilyl)alkanones – Intramolecular C/H Insertion of Siloxyalkylidenecarbene Intermediates

Thermal Decomposition of α‐Diazo‐α‐(trialkylsilyl)alkanones – Intramolecular C/H Insertion of Siloxyalkylidenecarbene Intermediates

Aryl Trialkylsilyl Ketenes: Acid‐Catalyzed Synthesis from 1‐Aryl‐2‐diazo‐2‐trialkylsilylethanones and Their Conversion into 3‐Silyl‐1‐silyloxyallenes

Triethylsilyl Trifluoromethanesulfonate

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