Imine salts from ammonia

Preparative Methods (i) preparation of racemic DPEN and its optical resolution Reaction of benzil and cyclohexanone in the presence of ammonium acetate and acetic acid at reflux temperature gives a cyclic bis-imine (1) (eq 1). Stereoselective reduction of the bis-imine with lithium in THF-liquid ammonia at —78 °C followed by addition of ethanol, then hydrolysis with hydrochloric acid and neutralization with sodium hydroxide produces the racemic diamine (2). Recrystallization of the l-tartaric acid salt from a 1 1 water-ethanol mixture followed by neutralization with sodium hydroxide, recrystallization from hexane results in (5,5)-DPEN (3) as colorless crystals. 

Schiff base complexes of lanthanides derived from -diketones and imines can be prepared [60] in acetone-water medium by dropwise addition of ammonia to adjust the pH to 5-6. In the absence of addition of ammonia simple adducts between lanthanide salt and imine are formed [61]. 

The original Kabachnik-Fields procedure employing ammonia as the amine component used ammonia in ethanol and the reactions were performed in sealed vessels at circa 100°C.90,123 This method avoids such conditions by using ammonium acetate as the source of ammonia, and it is also thought to act as an acid catalyst for imine formation other ammonium salts were unsatisfactory. Addition of water to produce a homogeneous reaction mixture resulted in diethyl 1-hydroxy-1-benzylphosphonate formation (i.e. from direct attack of diethyl phosphite 25 on benzaldehye, a common side reaction in the Kabachnik-Fields reaction). The yields of this reaction are serviceable, and better for aromatic than aliphatic aldehydes. The product 58 may be further purified by crystallization as the hydrochloride salt by treatment of 58 with hydrogen chloride in ethanol/diethyl ether.122... 

Amino-l,2-dithiolium salts are obtained from either / -oxocarbox-amides or ) -oxocarbonitriles by reaction with phosphorus penta-sulfide, followed by addition of perchloric acid (Scheme 6). These cations, which may also be considered as iminium salts, are deprotonated to the corresponding l,2-dithiol-3-imine by ammonia. ... 

Under acidic conditions, the desired amine formed is immediately protonated to give an ammonium salt, which is inhibited from participating in the amine exchange reaction. With added ammonia the intermediate imine will only participate in the exchange of nitrogen with the excess ammonia until its ultimate reduction to the primary amine. It is therefore possible to prepare mixed alkylamines by the addition of another amine prior to hydrogenation (Scheme 31). ... 

Aldehydes and ketones serve as useful precursors to amino acids when they are converted to a Schiff base (from aldehydes) or an imine (from ketones). Reduction of the imino C=N moiety, usually in situ, generates the amine. When 1.83 (m = 1, 2) was treated with ammonia, for example, the resulting iminium salt (1,84) was hydrogenated to give either 8-aminooctanoic acid (7.[Pg.18]

From the numerous ir-systems investigated, nitrogen-containing dienophiles are the most typical carbonyl derivatives for hetero Diels-Alder reactions. Simple imines, however, are quite unreactive and require highly reactive dienes as counterparts. - In contrast, electron-deficient species, such as iminium salts (134 Scheme 63) or N-acylimines (137 Scheme 64), do undergo [4 -t- 2] cycloadditions with normal nonactivated dienes. Thus, the intramolecular Diels-Alder reaction of the iminium species (134), created in situ from the aldehyde (133) and ammonia, gives the octahydroquinoline (135), which can be hydrogenated to afford the 8a-epimer of pumiliotoxin C (Scheme 63). ... 

The condensation of ketimines, prepared from 2-hydroxyacetophenones and primary amines, with R COaEt in the presence of LiH yields aminovinyl ketones 139 with y-arrangement of the NHR and R groups, which exist only in the open form. In an ethanol solution of HCl, these compounds cyclise to 2-(polyfluoroalkyl)-47f-chromene-4-iminium salts 140, which can be neutralised with ammonia to form 2-(polyfluoroalkyl)-4 (-chromene-4-imines 141. On treatment with aqueous acetic acid, compounds 139 and 141 are hydrolysed to chromanones 129, which can be easily converted into chromones 130 [63] (Scheme 43). 

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