Triethylamine A/-oxide

The standard oxidation procedure employs 30% hydrogen peroxide and 3 M sodium hydroxide. However, functionalities sensitive to strong alkali require milder conditions. In such cases, buffering, simultaneous addition of base and peroxide,492 or oxidation with Oxone ,493 triethylamine A-oxide,494-498 peracids,499,500 or sodium hypochlorite50 were recommended. Oxygen has been rarely used for such purpose,502 but trialkylboranes in bromoperfluorooctane were cleanly reacted with oxygen with the retention of configuration of the secondary alkylboranes (Equation (104)).503... 

One of the most commonly employed methods to promote the reaction is to add an amine A-oxide, such as triethylamine A-oxide or A-methylmor-pholine A-oxide.10-12 These A-oxides act by oxidising a CO ligand to C02 and creating a vacant site into which the alkene is able to bind. 

Methyl and 9-[(trimethylsilylmethyl)]-9-BBN derivatives are easily synthesized by the reaction of the corresponding lithium reagents with 9-methoxy-9-BBN. Unfortunately, such derivatives are spontaneously flammable in air, making them particularly hazardous to handle for the purpose of isolation. However, selective oxidation with anhydrous triethylamine A -oxide converts them to air-stable borinate esters which are efficient reagents for the methylation [149, 150] of haloalkenes or the syntheses of allylic and propargylic silanes (Scheme 2-52) [151]. 

The total synthesis of the sesquiterpene (+)-taylorione was achieved in the laboratory of J.G. Donkervoort who used the modified Pauson-Khand reaction to prepare the five-membered ring of the natural product. The preformed alkyne-cobalt complex was exposed to excess triethylamine-A/-oxide, which oxidized off two CO ligands to free up a coordination site for the ethylene. The optimum pressure of the ethylene gas had to be at 25 atm, and the reaction was conducted in an autoclave. 

Triethylamine, 61,83,87,88,94,99,100,112 Triethylamine A -oxide, 84 Triethylbenzylammonium chloride, 49 Triethylsilane, 104,127,128 Trifluoroacetic acid, 59 Tri methyl-m-dimethylaminophenylsilane, 40 Trimethyl orthoformate, 109... 

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

Treatment of y-nitrothioamides 368 with phenyl isocyanate and triethylamine (nitrile oxide generation conditions) leads to a.j3-unsaturated nitriles 369. The mechanism proposed for this reaction is shown in Scheme 1.42, which includes the dehydration stage of the nitrile oxide formed (418). 

The /V -hydroxylamino compounds (404) and (405), obtained from the reaction of tert-butyl acetate with 3,4-dihydroisoquinoline-A-oxide or 5,5-dimethyl-pyrroline-/V-oxide, when boiled in methylene chloride in the presence of triphenylphosphine, carbon tetrachloride and triethylamine, are transformed to (1,2,3,4- tetrahydroisoquinolin-l-ilidene) acetate (406) or (pyrrolidin-2-ilidene) acetate (407) (Scheme 2.181) (645). 

Problem 18.60 Synthesize the following compounds from alcohols of four or fewer C s, cyclohexanol and any needed solvents and inorganic reagents, (a) n-hexylamine, (h) triethylamine N-oxide, (c) 4-(N-methylamino)heptane, (d) cyclohexyldimethylamine, (e) cyclopentylamine, (/) 6-aminohexanoic acid. 

All of the usual chromium-based oxidation reagents that have been used for the oxidation of cyclobutanols to cyclobutanones, for example, chromium(VI) oxide (Jones reagent),302 pyri-dinium chlorochromate,304 pyridinium dichromate,307 and chromium(YI) oxide/pyridine (Collins),303 are reported to do so without any serious problems. Alternatively, tetrapropylam-monium perruthenate in the presence of A-methylmorpholine A -oxide. oxalyl chloride in the presence of triethylamine in dimethyl sulfoxide (Swern),158,309,310 or phenyl dichlorophos-phate in the presence of triethylamine and dimethyl sulfoxide in dichloromethane (Pfitzner-Moffatt),308 can be used. The Pfitzner-Moffatt oxidation procedure is found to be more convenient than the Swern oxidation procedure, especially with respect to the strict temperature control that is necessary to achieve good yields in the latter, e.g. oxidation of 1 to give 2.308... 

Oxidation of the pyridine nitrogen increases the propensity of the aromatic ring for nucleophilic attack at the 2- and 4-positions. a-Benzotriazolyl-substituted pyridines, quinolines, and isoquinolines may be prepared by treatment of the A -oxide with 1-tosylbenzotriazole in the presence of triethylamine in toluene or xylene under reflux <2001H1703> (Equation 78). 

Trithioles and 1,3,2-dioxathiolanes. 1,2,3-Trithiolanes are prepared by reaction of alkenes with elemental sulfur . The synthesis of 1,3,2-dioxathiolane -oxides (cyclic sulfites) and 1,3,2-dioxathiolane S, -dioxides (cyclic sulfates) is discussed in comprehensive reviews <1997AHC(68)89, 2000T7051>. The most widely used method for the preparation of 1,3,2-dioxathiolane A-oxides 557 is the reaction of the corresponding 1,2-diols 556 with thionyl chloride in the presence of pyridine or triethylamine (Scheme 251). More reactive 1,3,2-dioxathiolane S,A-dioxides 558 are usually obtained by oxidation of sulfites 557 with sodium periodate, which is mediated by ruthenium tetroxide generated in situ from a catalytic amount of ruthenium trichloride <1997AHC89, 2000T7051, CHEC-III(6.05.10.3)183>. 

One of the best activators fw dimethyl sulfoxide is the complex of sulfur trioxide/pyiidine, which in the presence of triethylamine rapidly oxidizes primary and secondary alcrdmls to aldehydes and ketones in very good yields at ambient temperature. This reagent also allows the very useM crmversion of allylic alcohols to the corresponding a, unsaturated carbonyl compounds. A further advantage of this procedure over many of the others is the ease of woiit-up, especially over the dimethyl sulfoxide-dicy-clohexylcarbodiimide method. 

OL-Bromo ketones. The reagent in combination with triethylamine converts oxides of alkenes and oxides of five- to seven-membered cycloalkenes into a-bromo ketones in 70-80% yield, Morpholinoenamines under these conditions are also converted into a-bromo ketones. 

The reaction of epoxy sulfonyl chlorides 136 with triethylamine is thought to proceed through intermediate epoxy sulfenes 137 to give the 5/7-1,2-oxathiole 2,2-dioxides 138 (Equation 26) <1998SL1411>. The interaction of phenylmethanesulfonyl chloride with triethylamine, 2,4,6-trimethylpyridine A -oxide, and an alkene probably involves epoxidation of phenylsulfene to give the hitherto unknown oxathiirane 3, 3 -dioxide (a-sultone) 139 which then adds to the alkene to afford the products 140 (Scheme 6) <2000CC189>. 

Enamines can be obtained as the products of the Polonovski reaction of amine oxides and, in particular, by reaction of piperidine A -oxides with acetic anhydride. This is primarily due to the fact that when acetate is the counterion the intermediate iminium ions are labile and readily tautomerize. The formation of enamines during the Polonovski reaction is also favored by the presence of a base. In fact, enamines are often obtained in high yield from the reaction of an IV-oxide with trifluoroacetic anhydride in the presence of triethylamine or pyridine. Conversion of intermediate iminium ions, generated under modi-fred Polonovski conditions, to enamine products can also occur during hydrolytic work-up. 

The enamino ketone (54) can also be prepared by a Polonovski approach, involving either sequential addition of wi-chloroperbenzoic acid, acetic anhydride and triethylamine to a cooled solution of (52) in methylene chloride or reaction of the A -oxide (53) with trifluoroacetic anhydride (Scheme 10). ° Although the latter approach involves three distinct steps, the overall yield of (54) is higher. 

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