Amines aryl, alkylation

Aliphatic and some aryl-alkyl tertiary amines... 

Nitrosation (Section 22.15) Nitrosation of amines occurs when sodium nitrite is added to a solution containing an amine and an acid. Primary amines yield alkyl diazonium salts. Alkyl diazonium salts are very unstable and yield carbo-cation-derived products. Aryl diazonium salts are exceedingly useful synthetic intermediates. Their reactions are described in Table 22.7. 

An aryl alkyl ketone 1 can be converted into an tn-arylalkane carboxylic amide 2 by employing the Willgerodt reaction The number of carbon centers is retained. The reaction is carried out by treating the ketone with an aqueous solution of ammonium polysulfide. A variant that has been developed by Kindler, and which is called the Willgerodt-Kindler reaction, uses a mixture of sulfur and a secondary amine instead of the ammonium polysulfide. 

Doyle et al. (1977 c) and Oae et al. (1980) reported modified Meerwein arylations with significant improvements in the yield by the use of aryl amines and alkyl nitrites in place of arenediazonium salts. However, good yields are only achieved if alkenes activated by electron-withdrawing groups are present. 

The dimerization of ketones to 1,2-diols can also be accomplished photochemi-cally indeed, this is one of the most common photochemical reactions. The substrate, which is usually a diaryl or aryl alkyl ketone (though a few aromatic aldehydes and dialkyl ketones have been dimerized), is irradiated with UV light in the presence of a hydrogen donor such as isopropyl alcohol, toluene, or an amine. In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n — k excitation, and the singlet species thus formed crosses to the T, state with a very high efficiency. 

SECTION 95 AMINES FROM ALKYLS, METHYLENES AND ARYLS... 

Ross and Chiarello (1979) have described a method for denitrosation of nitrosamines, such as dlalkylnitrosamines e.g. N-nitrosodimetl laminer etc., and complex aryl-alkyl nitrosamines, e.g. N-nitroso-N-(l-ethylpropyl)-3,4-dimethyl-2,6-dinitroaniline. The products of nitration and amination containing nitrosamlne as a substantial impurity are treated with an aldehyde or ketone in the presence of strong acids such as hydrochloric or hydrobromic acid. Under pressurized conditions at 105-110% for cme to two hours, the nitrosamlne is destroyed. The desired product can be recovered after neutralization of the excess acid. The equation shows the denitrosation of pendimethalin ... 

It is interesting to note that the oxidation of sulphoxides by peracids is faster in alkaline than in acidic solution. This is in contrast to the oxidation of sulphides and amines with the same reagents " . The oxidation rate of ortho-substituted aryl alkyl sulphoxides with aromatic peracids is less than the corresponding meta- and para-substituted species due to steric hindrance of the incoming peracid anion nucleophiles . Steric bulk in the alkyl group also has some effect . Such hindrance is not nearly so important in the oxidation reaction carried out under acidic conditions . 

In 1978 and 1980 the coupling of aryl bromides and iodides with both aliphatic and aromatic thiols was first reported in the presence of NaO-t-Bu and Pd(PPh3)4 (Equation (35)).118,119 In contrast to aryl halide aminations and etherifications, the thiation reactions did not require unusual catalysts. Yet, reactions that form aryl alkyl sulfides from alkyl thiols occurred in modest yields in many cases ... 

Michael-type addition of cyclic amines (piperidine, A-methylpiperazine) to thiazolo[3,2-A][l,2,4]triazole-5(6//)-ones 46 provides an easy entry to 2-aryl(alkyl)-6-(a-aminoarylmethyl)thiazolo[3,2- ][l,2,4]triazol-6(5//)-ones 207 (Equation 19) <1999AF1006, 2001AF470>. 

If combined with an alkaline or amine base (l-5equiv.) in MeOH under 10-50bar (1-5 x 10 hPa) of H2 and temperatures ranging from 25 to 50°C, all complexes catalyze the reduction of aryl alkyl ketones to the corresponding 1-arylalkanols. The role of the base was described by the authors as metal-assisted direct transfer of to the C=0 function , and higher rates were obtained... 

The first class of amine-based nucleophilic catalysts to give acceptable levels of selectivity in the KR of aryl alkyl. yec-alcohols was a series of planar chiral pyrrole derivatives 13 and 14, initially disclosed by Fu in 1996 [25, 26]. Fu and co-workers had set out to develop a class of robust and tuneable catalysts that could be used for the acylative KR of various classes of. yec-alcohols. Planar-chiral azaferrocenes 13 and 14 seemed to meet their criteria. These catalysts feature of a reasonably nucleophilic nitrogen and constitute 18-electron metal complexes which are highly stable [54-58]. Moreover, by modifying the substitution pattern on the heteroaromatic ring, the steric demand and hence potentially the selectivity of these catalysts could be modulated. 

Fu and co-workers expanded the scope of amine KR to include indolines [100], However, as the initial conditions developed for aryl alkyl i ec-amines were unsuc-cessfnl dne to the low nucleophilicity of the catalyst, a few structural modifications were introdnced. Hence, after screening varions catalysts and achiral acyl donors, the use of a bulky pentacyclopentadienyl-derived catalyst in conjunction with an... 

Aryl alkyl amines gave hydroxylamine 0-arylsulfonates when reacted with arylsul-fonyl peroxide. The products were later decomposed to azomethine and further hydrolysis results in the corresponding amine with one less carbon atom. Thus when p-methoxy-benzylamine was treated with p-nitrophenylsulfonyl peroxide at —78 °C in ethyl acetate, p-methoxybenzaldehyde and p-methoxyaniline were obtained . Cyclic amines with p-nitrophenylsulfonyl peroxide were converted to the Al-(p-nitrophenylsulfonyloxy)amine derivatives, which further rearranged to ring-expanded cyclic imines in good yields (equation 9 f. ... 

Amines are alkyl or aryl derivatives of NH,. Replacing one, two, or three H s of NH, gives primary (1°), secondary (2°) and tertiary (3°) amines, respectively. 

A wide variety of amines, including aryl alkyl amines, alkyl amines, and amino alcohols have been resolved on a multi-ton scale (Scheme 7.10) [7]. This method has been used with methyl ethers. For example the racemic (l-methoxy)-2-propylamine (R,S 19) can be separated to give the (S)-20 which is required for the synthesis of a corn herbicide (21) and produced at 2500 t/y [7, 30] (Scheme 7.11). 

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