Deamination hydride shifts

The occurrence of some substitution in the deamination of 2-amino-2-deoxy-/3-D-mannopyranosides131 152 (72), and its absence in the reaction of the a-D-pyranoside150 69, must be due to the steric effect of the axial anomeric substituent which (in the a-D-pyran-oside) hinders the approach of the nucleophile (water) to either the C-2 carbonium ion or to C-2 of the diazonium ion. The glucose and glucitol tentatively detected as minor products in the deamination of 72 (R = D-glucose residue and R = D-glucitol residue) presumably arose by way of a hydride shift of H-l to C-2. 2-Deoxy-D-glucono-1,5-lactone (75) was not detected, as it would probably have. o,... 

When hydride shifts occur in the deamination of axial amines, cleavage of ether or glycosidic functions may result. The small amount of glucose tentatively identified151 in the product of deamination of 6-0-(2-amino-2-deoxy-/3-D-mannopyranosyl)-D-glucose (72 see p. 47) can be attributed to the occurrence of a hydride shift of H-l to C-2. 

A number of cases have been found in which 1,2-hydride shifts occur with retention at CB. For example, (> ) -6- (ami nomethyl) -2-methyloctane (32) is deaminated in aqueous perchloric acid to give 2,6-dimethyloctan-6-ol in 35 percent yield. This product is formed with 41 percent retention at CB. No fully satisfactory explanation for the retention has been proposed.44... 

Deamination of 1 -aminopropane-1 -14C gives unscrambled 2-propanol and partially scrambled 1-propanol as shown in Equation 6.44. (The numbers at the carbons of the 1-propanol indicate the percentage of 14C found at each position.)119 The 2-propanol almost surely arises from a 1,2-hydride shift. 

Comparison of product distributions from cis- and m 5-precursors demonstrates clearly that there are practically no feasible common intermediates that allow a crossover between the two series. This is best shown from the total extent of hydride shift, which is very low for all six experiments with trans-simine and its derivatives (1.3 to > 2.2%), but high in the cw-series (>26% to >34% >14% for direct deamination). 4-( e Butyl)cyclohex-l-ene is an elimination product formed in relatively small amount (7.6-17%) from trans-compounds, but it is by far the dominant product in the cw-series (70-78%). In external substitution by acetate this result is reversed. Internal substitution accounts for 15.1-44% of products with the trans-... 

We assume that a mechanism via diazonium ions is not ruled out. See also Section 7.3 for the striking difference in the stereochemistry of deaminations starting with (Z)- and ( )-diazenolates. X = HO , ArNH-, RCOO HY=R COOH (solvent). For another position of [X---H ]-after a 2,1-hydride shift in such an ion pair, see Maskill and Whiting (1976, Scheme 2). 

The small amount of monodeuterated cyclopropane could have arisen by a carbene insertion but a 1,3-hydride shift to give an isomeric intermediate carbonium ion, which then partitioned to elimination products, was preferred. As supporting evidence for this shift, rather than the normal 1,2-rearrangements, which are usually observed under solvolytic conditions, an earlier investigation of the deamination of carbon-labelled /i-propylamine was cited. Labelled l- C-/i-propylamine gives l- C-n-propanol (92%) and 3- C-n-propanol (8%). This product distribution can be explained only by a 1,3-hydride shift, viz-... 

Two successive 1,2-hydride shifts can be ignored, as the initially formed secondary carbonium ion would give rise to some isopropanol. In addition, deamination of isopropylamine does not yield n-propanol. The intermediacy of a protonated cyclopropane is excluded as no label is found on the 2-carbon... 

Collins has also criticized an earlier assumption, that nitrogen is detached to yiekl exclusively reactive, so called hot carbocations which, unlike solvolytic cold ions, are far less selective and so result in a set of various products Hot ions were assumably formed without anchimeric assistance, the charge being localized. Collins has shown that the unusual properties of cations formed in deamination reactions are retained after several Wagner-Meerwein rearrangements and 6,1,2-shifts But hot carbocations must lose their energy after one 6,2-hydride shift resulting in normal carbocations Collins considers the intermediate carbo-... 

Deamination of the corresponding amine gives the allylic alcohol that results from a hydride shift as the main product, and the extent of cyclization is increased ... 

With educts containing an axially oriented LG at C-3, in addition to an intramolecular Sn2 reaction with an axially oriented hydroxy or acetamido group in a vicinal position (IS, Table 3, entries 1 [26] and 2 [30]), elimination and/or hydride shift (E or M/E, entries 3 [30],4 [31] and 6 [32]), as well as substitution with retention of configuration (AS, entries 7 and 8 [27b]) have been observed. For the transformation outhned in entry 4, 2,6-di-ferf-butyl-4-methylpyridine was used as acid scavenger, since pyridine per se in a similar reaction had caused Sn2 displacement (entry 5 [33]). Of special interest are the results from the deamination of methyl 3-amino-3-deoxy-/5-D-allopyranoside (entry 6), where the main reaction consists of direct Sn2 displacement with formation of methyl... 

Deamination of 2-amino-l,5-anhydro-2-deoxy-D-mannitol with nitrous acid gave principally l,5-anhydro-2-deoxy-D-e/ yt/fru-hex-3-ulose (68%), by migration of H-3, and some 2-deoxy-D-a/ a6/no-hexose (8%) and 1,5-anhydro-D-glucitol (6%). It was established that 2-deoxy-D-nrai>//in-hexose is formed via a hydride-shift mechanism, rather than by acid-catalysed hydration of D-glucal produced by an elimination pathway. 

Although the homoallylic- cyclopropylcarbinyl cyclization is well-precedented in carbonium ion chemistry (101, 102) there seem to be no reports of the direct cyclization of the tertiary 4-terpinenyl carbonium ion. However, deamination of cyclohex-3-enyl amine and solvolysis cyclo-hex-3-enyl tosylate gives exo- and n /o-bicyclo[3.1.0]hex-2-yl derivatives as 6—43% of the products resulting from nucleophilic capture (101, 103, 104). The modest yield of bicyclic products in these reactions apparently is the result of competing nucleophilic capture prior to cyclization and hydride shift to the 2-cyclohexenyl cation. More efficient cyclization occurs in the acetolysis of 2-bicyclo[2.2.2]oct-5-enyl tosylate (49) owing to the rigid boat-like conformation of the precursor (105). The high efficiency of the base-catalyzed cyclization of the epoxide of 4-iso-... 

Farcasiu, D., C. Kascheres, and L. H. Schavartz Nitrous Acid Deamination of 2-(Aminomethyl)cyclohexanol. The Question of a 1,3-Hydride Shift or Two Consecutive 1,2-Hydride Shifts. J. Amer. Chem. Soc. 94, 180 (1972). 

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