Imidate salts isomerization

The basic hydrolysis of imidate salt 118 takes a different course from that of imidate salt 112, yielding first only the amide rotamer 120B which is then slowly isomerized to the equilibrium mixture (ratio 3 1) of 120A and 120B. Treatment of the ester ammonium salt 119 under the same basic conditions gave directly the aminoalcohol 123. This result shows that the amino-ester 122 is not an intermediate in the basic hydrolysis of imidate 118. The formation of the amide rotamer 120B is therefore the result of the direct fragmentation of a tetrahedral intermediate whidh is formed from 118. 

Imidate salts hydrolysis, 118-144 syn and anti, 120 isomerization, 142 B-lactam, 142 Iminium salts, 211-221 Imino-ethers, 147 lodolactonization, 169 Ionic state of tetrahedral intermediates, 65, 105-106, 119 Ionophore A-23187, 13 Isochromane-3-one, 70 Isocyanate, 300 Isonitrile, 296... 

The basic hydrolysis of imidate salt 64 was carried out (33), and it gave a mixture of aminoester 65 (83%) and N-methylpiperidone (66) (17%). This result can be explained in the following way. Assuming that this salt exists as a mixture of the syn and anti forms 67 and 68 (Fig. 6), these two isomeric forms would give the tetrahedral conformers 69 and 70 respectively. Conformer 70 can yield the aminoester 65 with stereoelectronic control whereas conformer 69 cannot break down. Thus, 69 would either be converted into 70 and 71 by rotation of the ethoxy group or undergo a chair inversion to conformer 72. Interestingly, 71 as well as 70 which come from the rota-... 

Under basic conditions, the hydrolysis of imidate salt UZ, at 0°C gave a mixture (2 B) of the amidoalcohol rotamers 115A and USB as the kinetic products of the reaction. Isomerization followed to yield the equilibrium ratio (4 6) of USA and USB. Imidate first anti imidate salt which does not give the anticipated product, i.e. the aminoester U4. However, being a formate, thus a reactive ester, it is possible that under the reaction conditions. U recyclizes rapidly to give new tetrahedral intermediates which then yield a 2 B mixture of amide rotamers USA and USB. This was proven by showing that the treatment of ester ammonium salt U1 under the same basic conditions at 0°C led directly to a 2 8 mixture of USA and USB. 

The hydrolysis of the cyclic imidate salt 118 was also studied (15). The imidate salt JJS (R=(CH3>2CgH3 ) behaved in a completely different manner from the salt 112, Under acidic conditions, it yielded a =1. 1 mixture of ester ammonium salt Shd the amidoalcohol J 20. Again, the hydrolysis is a slow process, and it could be observed (at the beginning of the reaction) that the amidoalcohol was first formed as the least stable rotamer 1208 only. Rotamer 120B was then slowly isomerized to give an equilibrium mixture of 120A (67%) and 1208 (33%). 

Substituted azocine systems are much more stable than the parent compound, and 2-methoxy derivatives have been intensively examined. Starting from cyclohexa-1,4-diene (3), a [2 + 2] cycloaddition with chlorosulfonyl isocyanate, followed by removal of the chlorosulfonyl group, leads to the /3-lactam 4, which can be transformed by O-methylation with Meerwein s salt into the corresponding imidate. Monobromination with A-bromosuccinimide and subsequent treatment with base results in a methoxyazabicyclo[4.2.0]octatriene derivative, which spontaneously isomerizes to 2-methoxyazocine (5).13,14... 

A major distinction for nucleophilic reactions with ambident anions is whether they proceed with kinetic or thermodynamic control.80 N-Substituted saccharins (10) should be thermodynamically more stable because of amide character than the isomeric pseudosaccharin (3) of imidate structure. In fact 3 may be rearranged thermally to 10 in an irreversible reaction.96 The threshold for thermodynamic control appears to be lowered for electrophiles with multiple bonds, e.g., formaldehyde, reactive derivatives of carboxylic acids, but also quaternary salts of N-heterocyclic compounds.80 It will be seen that in those cases substitution indeed occurs at the nitrogen, not necessarily through thermodynamic control. 

The second cathodic process in [Ag(44e)2] Ag is broad and occurs at a very low potential (—0.5 V vs Ag/Ag+) compared to the other silver salts in this series. This anomalous behavior was attributed to the lower stability of the silver complex and the presence of several isomeric forms of the acyclic imide ligand. 

Aminoethyl)-l,2,4-oxadiazoles (606 R = alkyl or aryl) readily isomerize to 3-acylamino-2-pyrazolines (607) on heating. Treatment of the salt (608) with triethylamine yields the transient ylide (609), which decomposes to methyl-phenylcarbodi-imide (610). 2,3-Diphenyl-l,2,4-oxadiazolin-5-one (611) rearranges photochemically to a mixture of the oxadiazolinones (612) and (613) pyrolysis gives 2-phenylbenzimidazole with extrusion of carbon dioxide. The oxadiazole (614) rearranges thermally to the indazole (615). ... 

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