Alkyl, amines Synthesis

GABRIEL Amine Synthesis Synthesis ol primary amines from alkyl halides... 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

Primaty amines may be prepared from alkyl halides using phthalimide. This is called the Gabriel amine synthesis. 

Another alternative for preparing a primary amine from an alkyl halide is the Gabriel amine synthesis, which uses a phthalimide alkylation. An imide (—CONHCO—) is similar to a /3-keto ester in that the acidic N-H hydrogen is flanked by two carbonyl groups. Thus, imides are deprotonated by such bases as KOH, and the resultant anions are readily alkylated in a reaction similar to the acetoacetic ester synthesis (Section 22.7). Basic hydrolysis of the N-alkylated imide then yields a primary amine product. The imide hydrolysis step is analogous to the hydrolysis of an amide (Section 21.7). 

Gabriel amine synthesis (Section 24.6) A method for preparing an amine by SN2 reaction of an alkyl halide with potassium phthalimide. followed by hydrolysis. 

The direct reductive amination (DRA) is a useful method for the synthesis of amino derivatives from carbonyl compounds, amines, and H2. Precious-metal (Ru [130-132], Rh [133-137], Ir [138-142], Pd [143]) catalyzed reactions are well known to date. The first Fe-catalyzed DRA reaction was reported by Bhanage and coworkers in 2008 (Scheme 42) [144]. Although the reaction conditions are not mild (high temperature, moderate H2 pressure), the hydrogenation of imines and/or enam-ines, which are generated by reaction of organic carbonyl compounds with amines, produces various substituted aryl and/or alkyl amines. A dihydrogen or dihydride iron complex was proposed as a reactive intermediate within the catalytic cycle. 

In recent years, the importance of aliphatic nitro compounds has greatly increased, due to the discovery of new selective transformations. These topics are discussed in the following chapters Stereoselective Henry reaction (chapter 3.3), Asymmetric Micheal additions (chapter 4.4), use of nitroalkenes as heterodienes in tandem [4+2]/[3+2] cycloadditions (chapter 8) and radical denitration (chapter 7.2). These reactions discovered in recent years constitute important tools in organic synthesis. They are discussed in more detail than the conventional reactions such as the Nef reaction, reduction to amines, synthesis of nitro sugars, alkylation and acylation (chapter 5). Concerning aromatic nitro chemistry, the preparation of substituted aromatic compounds via the SNAr reaction and nucleophilic aromatic substitution of hydrogen (VNS) are discussed (chapter 9). Preparation of heterocycles such as indoles, are covered (chapter 10). 

The usefulness of this reaction for the preparation of heterocycles under mild conditions became apparent in 1978, when chemists from Merck, Sharp Dohme reported the synthesis of bicyclic 3-lactams by intramolecular carbene N-H insertion [1179]. Intramolecular N-alkylation of P-lactams by carbene complexes is one of the best methods for preparation of this important class of antibiotic and many P-lactam derivatives have been prepared using this methodology [1180 -1186] (Table 4.11). Intramolecular N-H insertion can also be used to alkylate amines [1187-1189], y-lactams [1190], and carbamates [1191-1193] (Table 4.11). 

Amine synthesis from reductive amination of a ketone and an amine in the presence of excess formic acid, which serves as the reducing reagent by delivering a hydride. When the ketone is replaced by formaldehyde, it becomes Eschweiler-Clarke reductive alkylation of amines. 

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). 

Soloshonok and co-workers have developed a method for the synthesis of a-(perfluoro-alkyl)amines from perfluoroalkyl carbonyl compounds by a transamination involving an azomethine a/omethine (Schiffbase) isomerization. They call this method a biomimetic, base-catalyzed 1,3-proton shift reaction, and have applied it to perfluoroaldehydes,12-15 perfluoroalkyl ketones,12 18 / -(perfluoroalkyl)-/l-oxo esters,15 16 19 24 and - -( perfluoroalkyl)-a-oxo es-ters2 " -26 to synthesize the corresponding a-(perfluoroalkyl)amincs, / -(perfluoroalkyl )-/i-amino acids, and 3 -(perfluoroalkyl)- x-amino acids. 

Alkylation of aziridines amine synthesis.3 N-Substituted aziridines (alkyl, benzyl, silyl, Boc) react with lithium dialkylcuprates in the presence of BF3 etherate (excess) with opening of the ring to give primary or secondary amines. 

The Zr-catalyzed asymmetric alkylation shown in Eq. (2) [8] illustrates two important principles (1) The catalytic asymmetric protocol can be readily applied to the synthesis of non-aryl imines to generate homochiral amines that cannot be prepared by any of the alternative imine or enamine hydrogenation protocols. (2) The catalytic amine synthesis involves a three-component process that includes the in situ formation of the imine substrate, followed by its asymmetric alkylation. This strategy can also be readily applied to the preparation of arylamines. The three-component enantioselective amine synthesis suggests that such a procedure maybe used to synthesize libraries of homochiral amines in a highly efficient and convenient fashion. 

In 2008, the same authors reported the synthesis of polyfunctionalized /V-alkyl-[S-lac tains with high stereoselectivity in an efficient manner performing the same reaction with allyl bromide and heteroarylidene N-alkyl-amines. Interestingly, by modulating the type of alkyl group linked to the nitrogen atom, it is possible to influence the reaction stereoselectivity [164]. 

Makino et al.35 developed a solid-phase synthesis of 1,3-disubstituted 2-thioxoquinazoline-4-ones using HMP Lanterns that were derivatized with a 4-aminobenzoate ester. Following the assembly of amide 25 (Scheme 9), SnAt reaction with alkyl amines gave support-bound products 26 with high conversion. The key thiocarbonylation step was achieved with thiocarbo-nyldiimidazole in decalin at 95° for 16 h in the presence of DMAP to afford 1,3-disubstituted 2-thioxoquinazoline-4-ones 27. The target compounds 28... 

So the reaction of an alkyl halide with NaSH or Na2S cannot usually be made to stop after one alkylation as the anion of the first product is at least as nucleophilic as HS or S2. This is obvious in reactions with Na2S. Less obviously with NaSH the first reaction 18 gives the thiol 19 but this is in equilibrium with RS- and a second displacement 20 gives the sulfide 21. We shall see shortly how to get round this problem. A more important example—the failure of the alkylation of ammonia to give a useful amine synthesis—has chapter 8 to itself. 

Amine synthesis needs a separate chapter because the C-X disconnection la used for ethers, sulfides and the like in chapter 4 is not suitable for amines. The problem is that the product of the first alkylation 2 is at least as nucleophilic as the starting material 1 (if not more so because of the electron-donating effect of each alkyl group) and further alkylation occurs giving the tertiary amine 3 or even the quaternary ammonium salt 4. It is no use adding just one equivalent of Mel as the first formed product 1 will compete with the starting material 2 for Mel. 

Darifenacin 63 is Pfizer s treatment for urinary urge incontinence. Disconnection at the C-N bond with some amine synthesis in mind (chapter 8) gives a much smaller heterocycle 64 that can again be disconnected in the middle with the idea of alkylating some enolate such as 65 with the derivative of an alcohol 66. This is attractive because 66 is available as a single enantiomer cheaply from the amino acid hydroxyproline.19... 

There remained the synthesis of 60. An old synthesis7 used essentially the strategy we have outlined via 65 alkylation of MeNH2 with the chloro-acetal 74, conjugate addition of 75 to butenone 76 and cyclisation in acid solution. It was very low yielding. One reason is the poor amine synthesis by alkylation (chapter 8) and another is presumably that the acetal 77 hydrolyses to the aldehyde 65 but control in the cyclisation is poor. 

It results in the formation of the corresponding borazinyl-N-alkyl-amine-boranes [BH3(CH3)2N(CH2)3NBH]3 when the reaction is carried out with only 6 molar equivalents of the diamine. Aromatic diamines have also been used in this synthesis 103>. Borazines with N-organosilicon substituents have been obtained by reacting silicon-containing nitriles, for example, 4-cyano-2,2,6,6-tetramethyl-2,6-disilatetrahydropyrane, with NaBH4 and BF3 in tetrahydrofuran. 

Moreover, reduction of alkyl aryl ketones can be used to access optically pure secondary aryl alkyl amines, as illustrated in an enantioselective synthesis of SDZ-ENA-713 (ll)60 and as we have demonstrated in a related process (Scheme 16.8). 

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