Reduction by tin

Betaines 261 are stable crystalline compounds. Knowledge of their chemical reactions is still limited. Alkaline hydrolysis of aryl derivatives (261 R = Ar) gives the 2-azobenzoic acids 266 but the mechanism of this rearrangement is unknown. Reduction by tin and hydrochloric acid gives the hydrazides 267. Thermolysis of the p-tolyl compound (261 R = p-MeC6H4) (120 C at 0.1 mm Hg) gives the isomeric triazine (268 R = >-MeC6H4). Phosphorus pentasulfide converts the 2-methyl derivative (261 R = Me) into 2-methyl l,2,3-benzotriazinium-4-thiolate (272 R = Me) (Section in,B,15). 

In contrast to the quinoline and isoquinoline series, thienopyridines are apparently resistant to reduction by tin-hydrochloric acid, since the parent systems can be obtained by reductive dehalogenation or chloro-derivatives. Quaternary salts are reduced to the JV-alkyl-4,5,6,7-tetra-hydrothienopyridine by sodium borohydride,45,48,89-91 and the azo-methine bond in dihydro derivatives (e.g. 69) is reduced by lithium aluminum hydride.47... 

Radical cyclization reactions have proven to be a very efficient approach for polycyclic natural product synthesis. In many cases, the last step involves a reduction of a cyclic radical with formation of a new stereogenic center. Very good stereochemical control has been achieved with such polycyclic radicals. For example, Beckwith has reported a highly stereoselective formation of a quinolizidine ring (Scheme 19, Eq. 19.1) [41b]. This process is the key reaction in a four-step synthesis of epilupinine and the stereochemical outcome results from a stereoselective axial reduction by tin hydride of a bicyclic radical. In a related process, Tsai has prepared silylated hydroxyquinolizidine by radical cyclization to an acylsilane followed by a radical-Brook rearrangement (Scheme 19, Eq. 19.2) [42]. 

In spite of some disadvantages, reduction with tin has found widespread use for preparative purposes, as has reduction by tin(n) chloride which is superior to use of the metal. Both reagents are nowadays being more and more replaced by modern catalytic methods. 

Arylaminostibinoxides may be obtained by hydrolysis of the dichlorides by sodium or ammonium hydroxide, and also by the nitration of unsubstitiited stibmic acids and subsequent reduction by tin and hydrochloric acid in the presence of acetic acid. 

In 1888, Foerster (91), reproducing the same reaction with dianisyl-thiourea, demonstrated that the compound he obtained (59) could lose a sulfur atom by reduction with tin and hydrochloric acid to form a product analogous to N-phenylpiperidine (60). 

Nitro groups are readily reduced to primary amines by a variety of methods Cat alytic hydrogenation over platinum palladium or nickel is often used as is reduction by iron or tin m hydrochloric acid The ease with which nitro groups are reduced is especially useful m the preparation of arylamines where the sequence ArH ArN02 ArNH2 IS the standard route to these compounds... 

The position of the free hydroxyl group in these two alkaloids is either C or C , since Spath has shown that the OiV-diacetyl derivative of -5-hydroxy-3 4-dimethoxyphenylethylamine, when heated in toluene solution with phosphoric oxide, yields a product which must be either 6-acetoxy-7 8-dimethoxy-, or 8-acetoxy-6 7-dimethoxy-l-methyl-3 4-dihydrowoquinoline. On reduction with tin and hydrochloric acid t is converted into anhalonidine, which must therefore be 6-hydroxy-7 8-dimethoxy- (or 8-hydroxy-6 7-dimethoxy-)-l-methyl-l 2 3 4-tetrahydrofsoquinoline. Similarly the methiodide of the acetoxy-com-pound on reduction yields, by loss of acetic acid and addition of two hydrogen atoms, pellotine, proving the latter to be A -methylanhalonidine. The position of the free hydroxyl group was finally shown by Spath to... 

The synthesis of meconin has been referred to already (p. 201). Cotarnine has been synthesised by Salway from myristicin (I) as a starting-point. This was transformed into jS-3-methoxy-4 5-methylenedioxy-phenylpropionic acid (II), the amide of which was converted by Hofmann s reaction into )S-3-methoxy-4 5-methylenedioxyphenylethylamine, and the phenylacetyl derivative (HI) of this condensed, by heating it in xylene solution with phosphoric oxide, giving rise to the two possible dihydroiso-quinoline derivatives. The first of these substances, 8-methoxy-6 7-methylenedipxy-1-benzyl-3 4-dihydroiioquinoline (IV), on conversion into the methochloride and reduction with tin and hydrochloric acid, gave... 

Solutions containing compounds of copper, tin, arsenic, antimony, and other reducible metals must never be used. These must be removed before the reduction by treatment with hydrogen sulphide. 

Reductant equivalent weights of, 847 Reduction 409 by chromium(II) salts, 409 by hydrogen sulphide, 416 by Jones reductor (zinc amalgam), 410 by liquid amalgams, 412 by silver reductor, 414 by sulphurous acid, 416 by tin(II) chloride, 415 by titanium(II[), 410 by vanadium(II), 410 see also Iron(III), reduction of Reduction potentials 66 Reference electrodes potentials, (T) 554 Relative atomic masses (T) 819 Relative error 134 mean deviation, 134... 

Aniline, 4,4 -azodi-, 40,18 Aniline, reaction with hexachlotoace-tone to form a, ,a-trichloro-acetanilide, 40, 103 reaction with maleic anhydride, 41,94 Anisoin, reduction to deoxyanisoin by tin and hydrochloric add, 40, 16... 

Reduction, see also Hydrogenation electrolytic, see Electrolysis of anisoin to deoxyanisoin by tin and hydrochloric acid, 40, 16 of aromatic compounds to dihydroaromatics by sodium and ammonia, 43, 23... 

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