Boronic oxidative amination

Boron halides, coordination compounds with amines, 5 26 Boron imide, condensed derivatives of, from boron halide-amine coordination compounds, 6 28 Boron oxide, porous, 2 22 Bromamide, di- (NHBr2), 1 62 analysis of, 1 64... 

The tri-2-phenylpropylborane formed can be oxidized and hydrolyzed to 2-phenylpropanol-l, thus representing [as with aluminum alkyls (146)] an overall anti-Markownikoff hydration of a-olefins. Besides employing trialkylboranes as a source of boron hydrides, similar additions have been accomplished by heating olefins with boron hydride-amine complexes. As the latter are not as oxygen-sensitive, they are easier to handle (73) ... 

Figure1.33 Oxidative amination of boronic acid derivatives.

Six categories of 7V-hetero atom derivatives are considered N-M (M = boron, copper), N-N (e.g., N-nitro, A-nitroso), N-oxides (used to protect teriary amines), N-P (e.g., phosphinamides, phosphonamides), N-SiR3 (R = CH3), and N-S (e.g., sulfonamides, sulfenamides). 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

Methoxycarbonylformonitrile oxide is smoothly generated by 3 -elimination of methanol from E -N-methoxy-N-(methoxycarbonylmethylene)amine N-oxide, MeC>2CCH=N(0Me)0, in the presence of a catalytic amount of boron trifluoride etherate (96). 

The relay compound 1025 required for the synthesis of all of these 7-oxygenated carbazole alkaloids was obtained starting from commercially available 4-bromo-toluene (1023) and m-anisidine (840) in two steps and 72% overall yield. Buchwald-Hartwig amination of 4-bromotoluene (1023) with m-anisidine (840) furnished quantitatively the corresponding diarylamine 1024. Oxidative cyclization of 1024 using catalytic amounts of palladium(ll) acetate afforded 3-methyl-7-methoxycarbazole (1025). Oxidation of 1025 with DDQ led to clauszoline-K (98), which, on cleavage of the methyl ether using boron tribromide, afforded 3-formyl-7-hydroxycarbazole (99) (546) (Scheme 5.149). 

The oxidation by amine oxides provides a basis for selection among non-equivalent groups on boron. In acyclic organoboranes, the order of reaction is tertiary > secondary > primary. In cyclic boranes, stereoelectronic factors dominate. With 9-BBN derivatives, for example, preferential migration of a C—B bond which is part of the bicylic ring structure occurs. 

The four-coordinate amine complexes are very stable to oxidation 34,143 they do not react with I2 and undergo only monosubstitution upon treatment with Br2 (equation 26). Monohalo-genation of bisamine complexes of the [H2BLL ]+ type affords cations containing chiral boron 34,148 the [XHB(NMe3)4-Mepy]+ (X = Cl, Br) cations were resolved149 into enantiomers. The crystal structure for X = Br has been reported.150... 

Based on the excellent solubility and reducing properties of amine boranes, they are often used for the stabilization and purification of industrial materials. Further, they are applied as additives in hydrocarbon fuels and in lubricating oils, as polymerization catalysts, as ingredients in photographic processing and in the electroplating industry.169 High stability towards hydrolysis and oxidation makes cationic boron chelates useful as water-soluble dyes.170... 

The orf/to-formylation of 2-aminopyridines can be effected via the rearrangement of the azasulfonium salt prepared from a 2-aminopyridine, 1,3-dithiane, f-butyl hypochlorite and sodium methoxide (74CC685). The crude sulfilimine (815) was refluxed in f-butanol containing potassium f-butoxide to yield the dithioacetal (816). Hydrolysis of (816) with mercury(II) oxide/boron trifluoride etherate gave the aldehyde (817 Scheme 191). This method should be applicable to the formylation of other heterocyclic amines. 

In the approach of Snieckus [51] (Scheme 32), 201 was obtained in one step by palladium(0) promoted coupling of the known boronic acid 208 and 7-iodoindoline 209. The latter was prepared from N-acetylindoline via iodination of its 7-thallo derivative followed by hydrolysis of the resulting iodoamide. The initial product of coupling, the carbinol amine 210 readily suffered aerial oxidation to 201, which on dehydrogenation yielded 202. 

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