Nitrogen hydrides anionic

Nitrogen heterocycles more electrophilic than benzene are susceptible to attack by hydride ion from a complex metal hydride anion. In protic solvents the intermediate cyclic enamines can undergo further reduction. The proper choice of reducing agent and reaction conditions thus allows the preparation of many partially reduced nitrogen heterocycles unavailable by other routes. These reduction procedures provide a valuable adjunct to catalytic hydrogenation155 for the syntheses of saturated nitrogen heterocycles. 

The sequence of steps presented assumes an electrofugal (from the point of view of the substituted atom Cl) opening of the cycle for elimination and it forces the hydride anion to leave the nitrogen atom. This concerns not only acrylonitrile formation 29, but also formation of beta-hydroxypropionitrile 28. 

Deprotonation of Al,<9-bis(trimethylsilyl)hydroxylamine with n-butyllithium or potassium hydride at low temperature yields the nitrogen centered anion Al,<9-bis(trimethylsilyl)hydroxyl-amide. At higher temperatures the oxyanion Al,A -bis(tri-methylsilyl)hydroxylamide is formed by rearrangement. Each reacts with acyl chlorides chemospecifically by M-acylation and 0-acylation, respectively. The oxyanion also reacts with silyl halides, methyl iodide, and sulfonyl chlorides chemospecifically on oxygen. In a Peterson-type one-pot reaction, oximes and oxime derivatives can be prepared effectively from the N-anion of iV,0-bis(trimethylsilyl)hydroxylamine and an aldehyde or ketone (eq 5). Oximes of sterically hindered ketones can be formed in high yields by this procedure. 

Reduction by hydride transfer (H" = H + 2e ) occurs when the osmium cluster [Os3( -H)2(CO)io] is reacted with a whole variety of organoazides the hydride anion is transferred to the terminal nitrogen atom N3 and a monoanionic organoazide fragment is... 

According to a detailed mechanistic study, the first step is the abstraction of the relatively acidic hydrazone proton (93- 97). This is followed by hydride attack on the trigonal carbon of the C=N bond, mainly from the a-side at C-3, together with the concomitant loss of the tosylate anion (97 -> 98). Expulsion of nitrogen from the resulting intermediate (98) yields a fairly insoluble anion-metal complex (99) which upon decomposition with water provides the methylene derivative (100). 

Nitrogen forms more than 20 binaiy compounds with hydrogen of which ammonia (NH3, p. 420), hydrazine (N2H4, p. 427) and hydrogen azide (N3H, p. 432) are by far the most important. Hydroxylamine, NH2(OH), is closely related in structure and properties to both ammonia, NH2(H), and hydrazine, NH2(NH2) and it will be convenient to discuss this compound in the present section also (p. 431). Several protonated cationic species such as NH4+, N2H5+, etc, and deprotonated anionic species such as NH2 , N2H3 , etc. also exist but ammonium hydride, NH5, is unknown. Among... 

Of the several syntheses available for the phenothiazine ring system, perhaps the simplest is the sulfuration reaction. This consists of treating the corresponding diphenylamine with a mixture of sulfur and iodine to afford directly the desired heterocycle. Since the proton on the nitrogen of the resultant molecule is but weakly acidic, strong bases are required to form the corresponding anion in order to carry out subsequent alkylation reactions. In practice such diverse bases as ethylmagnesium bromide, sodium amide, and sodium hydride have all been used. Alkylation with (chloroethyl)diethylamine affords diethazine (1), a compound that exhibits both antihista-minic and antiParkinsonian activity. Substitution of w-(2-chloroethyl)pyrrolidine in this sequence leads to pyrathiazine (2), an antihistamine of moderate potency. 

The hydrogeh atom bound to the amide nitrogen in 15 is rather acidic and it can be easily removed as a proton in the presence of some competent base. Naturally, such an event would afford a delocalized anion, a nucleophilic species, which could attack the proximal epoxide at position 16 in an intramolecular fashion to give the desired azabicyclo[3.2.1]octanol framework. In the event, when a solution of 15 in benzene is treated with sodium hydride at 100 °C, the processes just outlined do in fact take place and intermediate 14 is obtained after hydrolytic cleavage of the trifluoroacetyl group with potassium hydroxide. The formation of azabi-cyclo[3.2.1]octanol 14 in an overall yield of 43% from enone 16 underscores the efficiency of Overman s route to this heavily functionalized bicycle. 

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