The Inductive Effects of Alkyl Groups as Determined by Desilylation Reactions

Benkeser, Robert A.; Hickner, Richard A.; Hoke, Donald I.

doi:10.1021/ja01542a062

Cited by 23 publications

(6 citation statements)

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“…[33] More recently,s everal cases of metal-promoted SiÀCb ond ruptures have been disclosed for both C sp 2 and C sp 3 carbon atoms. Although not common, the rupture of SiÀC bonds has already been documented under other circumstances.…”

Section: Resultsmentioning

confidence: 99%

“…The cleavage of SiÀCb onds under acidic conditions has long been known. [33] More recently,s everal cases of metal-promoted SiÀCb ond ruptures have been disclosed for both C sp 2 and C sp 3 carbon atoms. For instance, the lutetium hydride [(C 5 Me 5 ) 2 Lu(m-H)] 2 was reported to cleave the SiÀC sp 2 bond in PhSiH 3 to generate benzene and cross-linked polysilanes (SiH x ) y .…”

Section: Resultsmentioning

confidence: 99%

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Sequential Barium‐Catalysed N−H/H−Si Dehydrogenative Cross‐Couplings: Cyclodisilazanes versus Linear Oligosilazanes

Bellini

Roisnel

Carpentier

et al. 2016

Chemistry A European J

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Starting from Ph SiH, the barium precatalyst Ba[CH(SiMe ) ] ⋅(THF) was used to produce the disilazane Ph SiN(Bn)SiPh NHBn (4) by sequential N-H/H-Si dehydrogenative couplings with BnNH and Ph SiH . Substrate scope was extended to other amines and hydrosilanes. This smooth protocol gives quantitative yields and full chemoselectivity. Compound 4 and the intermediates Ph SiNHBn and Ph SiN(Bn)SiHPh were structurally characterised. Further attempts at chain extension by dehydrocoupling of Ph SiH with 4 instead resulted in cyclisation of this compound, forming the cyclodisilazane c-(Ph Si-NBn) (5) which was crystallographically authenticated. The ring-closure mechanism leading to 5 upon release of C H was determined by complementary experimental and theoretical (DFT) investigations. Ba[CH(SiMe ) ] ⋅(THF) and 4 react to afford the reactive Ba{N(Bn)SiPh N(Bn)SiPh } , which was characterised in situ by NMR spectroscopy. Next, in a stepwise process, intramolecular nucleophilic attack of the metal-bound amide on the terminal silicon atom generates a five-coordinate silicate. It is followed by turnover-limiting β-C H transfer to barium; this releases 5 and forms a transient [Ba]-Ph species, which undergoes aminolysis to regenerate [Ba]-N(Bn)SiPh N(Bn)SiPh . DFT computations reveal that the irreversible production of 5 through such a stepwise ring-closure mechanism is much more kinetically facile (ΔG =26.2 kcal mol ) than an alternative σ-metathesis pathway (ΔG =48.2 kcal mol ).

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Sequential Barium‐Catalysed N−H/H−Si Dehydrogenative Cross‐Couplings: Cyclodisilazanes versus Linear Oligosilazanes

Bellini

Roisnel

Carpentier

et al. 2016

Chemistry A European J

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“…and t.1.c. properties) with an authentic sample whose preparation was described above; and (ii) the title compound (9) (1 H, d, J 1.7 Hz); m / z 295 ( M + , loo%), 280 (99), 266 (lo), 252 (17), and 250 (26). l-Methyl-3-trimethylsilyl-9H-carbazol-2-ylmethunol.-Lithium aluminium hydride (28 mg, 0.74 mmol) was added to a solution of the carbazole (6) (123 mg, 0.38 mmol) in dry THF ( 5 ml) under nitrogen, and the mixture heated under reflux for 36 h. The excess of lithium aluminium hydride was destroyed by careful addition of water (0.5 ml) after which solid sodium hydrogen carbonate was added until a white grannular precipitate resulted.…”

Section: Ethyl L-methyl-9h-carbazole-2-carboxylatementioning

confidence: 99%

“…and t.1.c.) with the sample described above; (ii) ethyl 5-acetyl-3-hydroxy- (20).-Tetrachloroethane (4 ml) was added to a well mixed mixture of aluminium trichloride (70 mg, 0.52 mmol) and carbazole (17) (60 mg, 0.24 mmol) under nitrogen and the reaction mixture heated under reflux for 1.5 h. After cooling to room temperature the mixture was poured into dilute hydrochloric acid ( 1 ~; 20 ml) and the aqueous mixture extracted with ethyl acetate. The combined extracts were washed with water and brine, dried (MgSO,), and concentrated to give a yellow-green solid which was chromatographed (ether-light petroleum) to give the title compound (20) (20 mg, 0.08 mmol), potassium carbonate (60 mg, 0.43 mmol), and methyl iodide (0.5 ml) in acetone ( 5 ml) was heated under reflux under nitrogen for 5 h. The mixture was evaporated and the residue dissolved in water (10 ml) and extracted with ether.…”

Section: Reaction Of Ethyl 3-hydroxy-l-methyl-9h-carbazole-2-carboxyl...mentioning

confidence: 99%

Diels-Alder reactivity of pyrano[3,4-b]indol-3-ones. Part 4. Synthesis of the carbazole alkaloids carbazomycin A and B and hyellazole

Moody¹,

Shah²

1989

J. Chem. Soc., Perkin Trans. 1

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The first synthesis of the carbazole alkaloids carbazomycins A and B (1) is described. The key step is the regioselective Diels-Alder reaction between 1 -methylpyrano [3,4-61 indol-3-one (4) and ethyl trimethylsilyl propynoate to give ethyl 1 -methyl-3-trimethylsilylcarbazole-2-carboxylate (6). The ester and trimethylsilyl groups in carbazole ( 6 ) are converted into methyl and methoxy groups respectively, and the final oxygen substituent is introduced, after protection of the carbazole nitrogen, by bromination, lithiation, formation of the corresponding borate, and oxidation. The carbazole alkaloid hyellazole (3a) is synthesised by a similar route from 1 -phenylpyrano[3,4-61 indol-3-one.The carbazomycins (l), isolated from Streptouertcillium, are the first antibiotics which contain the carbazole nucleus. The structure of carbazomycin B (1 b) was determined by extensive 'H and ' 3C n.m.r. studies, and was unequivocally confirmed to be 4-hydroxy-3-methoxy-1,2-dimethylcarbazole (1 b) by an Xray crystallographic analysis.2 Carbazomycin A was postulated to be 3,4-dimethoxy-1,2-dimethylcarbazole (la), by analogy with carbazomycin B, together with spectroscopic analysis, and chemical conversion of carbazomycin B into carbazomycin A with diazomethane. Carbazomycin B was found to be active against certain types of phytopathogenic fungi, and also showed rather weak antibacterial and anti-yeast activities. Carbazomycin A, however, showed only very weak antifungal and antibacterial activity." Since the isolation of carbazomycins A and B in 1980, another six members of the carbazomycin family, designated as carbazomycins C-H, have recently been isolated from the same Streptomjxes specie^.^ Y ( l a ) X = Y = OMe (carbazomycin A) (1 b ) X = OMe, Y = OH (carbazomycin B) (2a) X = H, Y = OMe (3-deoxycarbazomycin) (2b) X = OMe, Y = H (4-deoxycarbazomycin) xQJ--=-oMe Me

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“…Although bromination of the carbazole (8) with N-bromosuccinimide (NBS) in acetonitrile gave the corresponding 6bromo compound (82%), bromination of the N-t-butoxycarbonylcarbazole (9) under the same conditions gave the required 4-bromo derivative (10) in excellent yield (95%). Treatment of the bromide (10) with t-butyl-lithium in tetrahydrofuran (THF) at -78 OC, followed by reaction of the resulting aryl-lithium with trimethyl borate, and alkaline hydrogen peroxide work-up gave the 4-hydroxycarbazole (1 1) (73%).…”

Section: ( 8 ) R =Me (2) R = P Hmentioning

confidence: 99%