Oxidative trimethylsilyl cyanide

Reactions of Heterocyclic N-Oxides with Trimethylsilyl Cyanide, Trimethylsilyl Azide, Trimethylsilyl Isothiocyanate, and Trimethylsilyl Halides... 

In two publications [36, 37] and a subsequent review [38], a closely related alternative procedure for conversion of pyridine-N-oxides into cyanopyridines was reported in 1983. This used a combination of the mild Lewis acid Me2NCOCl and trimethylsilyl cyanide 18 for the cyanation of pyridine N-oxides such as 860, affording, in CH2CI2, via 932 and 933, 2-cyanopyridine 862 in 94% yield and apparently no 4-cyanopyridine 864 [36-38] (Scheme 7.13). With 3-substituted pyridine N-oxides such as methyl nicotinate N-oxide a mixture of 40% methyl 2-cyanonico-tinate and 60% methyl 6-cyanonicotinate is obtained. 

Because allyltrimethylsilane 82 or benzyltrimethylsilane 83 can be regarded as combinations of the hard trimethylsilyl cation and the soff allyl or benzyl anions, pyridine N-oxide 860 reacts with excess 82 or 83 in the presence of catalytic amounts of tetrabutylammonium fluoride di- or trihydrate in THF to give 2-allyl-or 2-benzylpyridines 948 and 950 [60]. The general reaction of silicon reagents such as 82 and 83 or of trimethylsilyl cyanide 18 with fluoride to generate allyl or... 

Reactions of Nitrones and Aliphatic N-Oxides with Trimethylsilyl Cyanide 161... 

Strecker reactions provide one of the most efficient methods for the synthesis of a-amino nitriles, which are useful intermediates in the synthesis of amino acids and nitrogen-containing heterocycles. Although classical Strecker reactions have some limitations, use of trimethylsilyl cyanide (TMSCN) as a cyano anion source provides promising and safer routes to these compounds.133-351 Consequently, we focused our attention on tributyltin cyanide (Bu3SnCN), because Bu3SnCN is stable in water and is also a potential cyano anion source. Indeed, the Strecker-type reactions of aldehydes, amines, and Bu3SnCN proceeded smoothly in water (Eq. 9).1361 It should be noted that no surfactants are required in this reaction. Furthermore, Complete recovery of the toxic tin compounds is also possible in the form of bis(tributyltin) oxide after the reaction is over. Since conversion of bis(tributyltin) oxide to tributyltin cyanide is known in the literature, this procedure provides a solution to the problem associated with toxicity of tin compounds. 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

Photo-oxidation of l,l-dialkyl-2-arylhydrazines by single-electron transfer with trimethylsilyl cyanide (TMSCN) as cyanide ion source leads to regio- and stereoselective a-hydrazino nitriles. This stereoselective cyanation of hydrazines takes place on the more substituted carbon atom compared with the results obtained with tertiary amines (Scheme 5). 

Olefination of the Aldehyde 178 using a stabilized Wittig reagent followed by protecting group chemistry at the lower branch and reduction of the a,p-unsaturated ester afforded the allylic alcohol 179 (Scheme 29). The allylic alcohol 179 was then converted into an allylic chloride and the hydroxyl function at the lower branch was deprotected and subsequently oxidized to provide the corresponding aldehyde 161 [42]. The aldehyde 161 was treated with trimethylsilyl cyanide to afford the cyanohydrin that was transformed into the cyano acetal 180. The decisive intramolecular alkylation was realized by treatment of the cyano acetal 180 with sodium bis(trimethylsi-lyl)amide. Subsequent treatment of the alkylated cyano acetal 182 with acid (to 183) and base afforded the bicyclo[9.3.0]tetradecane 184. 

NMO NMP Nu PPA PCC PDC phen Phth PPE PPTS Red-Al SEM Sia2BH TAS TBAF TBDMS TBDMS-C1 TBHP TCE TCNE TES Tf TFA TFAA THF THP TIPBS-C1 TIPS-C1 TMEDA TMS TMS-C1 TMS-CN Tol TosMIC TPP Tr Ts TTFA TTN N-methylmorpholine N-oxide jV-methyl-2-pyrrolidone nucleophile polyphosphoric acid pyridinium chlorochromate pyridinium dichromate 1,10-phenanthroline phthaloyl polyphosphate ester pyridinium p-toluenesulfonate sodium bis(methoxyethoxy)aluminum dihydride (3-trimethylsilylethoxy methyl disiamylborane tris(diethylamino)sulfonium tetra-n-butylammonium fluoride f-butyldimethylsilyl f-butyldimethylsilyl chloride f-butyl hydroperoxide 2,2,2-trichloroethanol tetracyanoethylene triethylsilyl triflyl (trifluoromethanesulfonyl) trifluoroacetic acid trifluoroacetic anhydride tetrahydrofuran tetrahydropyranyl 2,4,6-triisopropylbenzenesulfonyl chloride 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane tetramethylethylenediamine [ 1,2-bis(dimethylamino)ethane] trimethylsilyl trimethylsilyl chloride trimethylsilyl cyanide tolyl tosylmethyl isocyanide meso-tetraphenylporphyrin trityl (triphenylmethyl) tosyl (p-toluenesulfonyl) thallium trifluoroacetate thallium(III) nitrate... 

Reaction of 4,5-disubstituted imidazole 1-oxide with trimethylsilyl cyanide (TMSCN) leads to 2-cyanoimidazole. If devoid of substituents at C4 and C5, the cyano (CN) group also enters these positions (1996JOC6971). The reactivity of the 2-, 4-, and 5-position is comparable and 245 reacts with TMSCN affording the isomeric cyanoimidazoles 296-298 in a ratio that depends on the nature of the 3-substituent, solvent polarity, and reaction temperature. These parameters could be optimized to give each of the three cyano compounds as the major product. Mechanisms (iii) and (iv) (Section 1.5.1.3 and 1.5.1.4) account for the formation of 296-298 (Scheme 88). 

Cyanosilylation of methyl ketones has been carried out using diphenylmethylphos-phine oxide and trimethylsilyl cyanide, generating a phosphorus isonitrile-type species, Ph2MeP(OTMS)(N=C ), as the reactive intermediate.271 A chiral oxazaborolidinium ion catalyst renders the reaction enantioselective. 

Two other types of catalysts have been investigated for the enantioselective Strecker-type reactions. Chiral N-oxide catalyst 24 has been utilized in the trimethylsilyl cyanide promoted addition to aldimines to afford the corresponding aminonitriles with enantioselectivities up to 73% ee [14]. Electron-deficient aldimines were the best substrates, but unfortunately an equimolar amount of catalyst 24 was used in these reactions. The asymmetric Strecker addition of trimethylsilyl cyanide to a ketimine with titanium-based BINOL catalyst 25 gave fast conversions to quarternary aminonitriles with enantiomeric excesses to 59%... 

An important application of oxidation of a C-H bond adjacent to a nitrogen atom is the selective oxidation of amides. This reaction proceeds in the presence of ferf-BuOOH as the oxidant and Ru(II) salts. Thus in the example of Eq. (36), the a-tert-butylperoxy amide of the isoquinoline was obtained, which is an important synthetic intermediate for natural products [138]. This product can be conveniently reacted with a nucleophile in the presence of a Lewis add. Direct trapping of the iminium ion complex by a nudeophile was achieved in the presence of trimethylsilyl cyanide, giving a-cyanated amines as shown in Eq. (37) [45]. This ruthenium/peracid oxidation reaction provides an alternative to the Strecker reaction for the synthesis of a-amino acid derivatives since they involve the same a-cyano amine intermediates. In this way N-methyl-N-(p-methoxyphenyl) glycine could be prepared from N,N-dimethyl-p-methoxyaniline in 82% yield. 

Reissert compounds have been prepared from compounds (21) and (23) using either trimethylsilyl cyanide or potassium cyanide as the cyanating agents. Yields ranged from 57% to 71 % <84JHCl 119, 86JHC545). The N-oxides of some thieno[2,3-6]pyridine derivatives, as shown in Equation (8), have been used in the Reissert-Henze reaction to produce cyano-substituted products <83JHC213>. 

Indole-3-carboxaldehydes gave the corresponding cyanohydrin silyl ethers 137 upon heating with trimethylsilyl cyanide in acetonitrile or DME. After subsequent oxidation with DDQ, good yields of the carbonyl nitriles 138 were obtained, also providing a mild new route for the parent system 138 (R1 = R2 = H). Further elaboration provided the imidates 139, which participated in a reaction with tryptophan esters to give moderate yields of the marine alkaloids rhopaladins A-D <02T2813>. 

In addition, l-benzyl-4-methyl-2-piperazinol (213) reacted with trimethylsilyl cyanide and boron trifluoride etherate to give l-benzyl-4-methyl-2-piperazinecar-bonitrile (214) (72% after separation from an isomer), which underwent partial dehydrogenation by m-chloroperoxybenzoic acid to afford 1 -benzyl-4-methyl-1,4,5,6-tetrahydro-2-pyrazinecarbonitrile (214a) in 53% yield 822 also, the oxime, 3-amino-6-hydroxyiminomethyl-2-pyrazinecarbonitrile 4-oxide (215) underwent... 

Phenylquinazoline-2-carbonitrile (mpl27 129°C) is prepared in good yields from 4-phenylquinazoline 1-oxide by treatment with trimethylsilyl cyanide in the presence of 1,8-diaza-bicycio[5.4.0]undec-7-ene or triethylamine as a base. ... 

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