Pyridines reactions with boranes

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

Amine-borane complexes are not very reactive toward hydroboration, but the pyridine complex of borane can be activated by reaction with iodine.160 The active reagent is thought to be the pyridine complex of iodoborane. 

The p-anisyloxymethyl group520 (abbreviated AOM) played an important role in the synthesis of Calicheamicinone reported by Clive and co-workers.521 Its removal from the sensitive multifunctional substrate 285 1 [Scheme 4.285] was accomplished with CAN in a mixture of pyridine, methanol and water. The excellent yield (89%) attests to the mildness of the conditions. Attempts to apply the same conditions to the deprotection of an AOM group from 286 1 [Scheme 4.286]522 failed but the deprotection was successful if it was conducted in the presence of 2,6-pyridinedicarboxylic acid N-oxide — conditions previously used to convert a phenol methyl ether to a quinone.523 AOM ethers undergo easy reductive cleavage to the corresponding methyl ethers with borane in toluene — a reaction that could have synthetic value when simple O-methylation procedures fail. 

Reactions of pyridylboranes with l-bromo-2-phenylethyne give the alky-nylated product 254 (84H2475). An analogous series of reactions has been described in pyridine halides with diethyl(4-isoquinolinyl)borane as substrate for the preparation of255. The reactions proceed in the same manner with comparable product yields (87H1603). 

Stirring a mixture of 2-formylamino-3-nitropyridine, benzaldehyde and borane pyridine complex in methylene chloride and acetic acid at room temperature afforded 1-benzyl-IbP. Similar derivatives of IbP were prepared from other aldehydes. The reaction of 3-benzylidenamino-2-formylaminopyridine with borane pyridine complex also led to the formation of benzyl-IbP (95JOC960). 

Pyridine-substituted nicotines, nornicotines, and anabasines are available from a-cyano-amines by a new synthesis. The syntheses of ( )-[l - N]nornicotine and ( )-[l - N]nicotine have been described, from cyclopropyl 3-pyridyl ketone and [ N]formamide. 4-Methylnicotine has been prepared it shows no nicotine-like pharmacological activity. " An investigation into the stereochemical factors involved in the behaviour of nicotine and related compounds in the Menschutkin reaction has been conducted.A bridged nicotine , 1,2,3,5,6,10b-hexahydropyrido[2,3-g]indolizine (44), has been synthesized by carboxylation of the dilithium derivative of 2-methylnornicotine followed by cyclisation and reduction with borane in tetrahydrofuran. Several 5-halogeno-nicotines have been prepared and their pK values and biological activities measured. ... 

In the case of terpyridine and acridine derivatives, the bis(methylamines) are the most convenient intermediates. Substituted 4 -phenyl-2,2 6 2 -terpyridines were prepared by reacting ( )-propenons and A/ -[2-(pyrid-2 -yl)-2-oxoethyl]pyridinium iodide with ammonium acetate in acetic acid or in methanol. The terminal pyridine moieties were oxidized with 3-chloroperbenzoic acid to A/, A/ "-dioxides followed by modified Reisserty-Henze reaction to obtain 6,6"-dicarbonitriles. The bis(methylamines) were obtained by reduction of the 6,6"-dicarbonitriles with borane (scheme 8 (Mukkala et al., 1993)). 

The preparation of fluorescent labelled glucitol, mannitol, maltitol and maltotriol derivatives by reaction of the corresponding free sugars with 2-amino-6-carboxyethyl pyridine or 2-amino-6-cyanoethyl pyridine, followed by reduction of the imine with borane, has been reported. ... 

Other methods for the preparation of 6.99 from leucine involved reduction of the acid moiety with borane and then oxidation to an aldehyde with chromium irioxide and pyridine. Another variation added zinc bromide to the enolate condensation reaction,75 which led to greater selectivity for the anti diastereomer. 

Reaction scope Despite attempts to date to achieve a dearomatization and hydrosilylation of heteroaromatics with magnesium catalysts faiUng to achieve turnover, the hydroboration of pyridine and alkyl and aryl substituted pyridines along with quinoline and isoquinoline with pinacol-borane catalyzed by 5-10 mol% [((ArNCMe)2CH Mg"Bu] has been reported (Scheme 18) [126]. 

Aldehydes and ketones have been converted to sulfides by treatment with thiols and pyridine-borane, RCOR -I- R"SH —+ RR CHSR", in a reductive alkylation reaction, analogous to 16-6. 

The BH3 molecule is not stable as a separate entity. This molecule can be stabilized by combining it with another molecule that can donate a pair of electrons (indicated as ) to the boron atom to complete the octet (see Chapter 9). For example, the reaction between pyridine and B2H6 produces C5H5N BH3. Another stable adduct is carbonyl borane, OC BH3 in which a pair of electrons is donated from carbon monoxide, which stabilizes borane. In CO, the carbon atom has a negative formal charge, so it is the "electron-rich" end of the molecule. Because the stable compound is B2H6 rather than BH3, the bonding in that molecule should be explained. 

In an effort to prepare bidentate boranes as colorimetric anion sensors, the incorporation of chromophoric boron moieties has also received attention. Reaction of lO-bromo-9-thia-lO-boranthracene 33 with dimesityl-1,8-naphthalenediylborate 26 affords diborane 34 (Scheme 14). This bright yellow diborane is soluble in chloroform, THF and pyridine. It has been fully characterized but its X-ray crystal structure could not be determined experimentally. Its structure was computationally optimized using DFT methods (B3LYP, 6-31 + G for the boron and sulfur... 

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