N rearrangement

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

A related reaction is the oxa-di-n-methane rearrangement, where one of the C=C double bonds is replaced by a C=0 double bond. The substrates are thus /3,y-unsaturated ketones. The rearrangement proceeds from the triplet state. This oxa-variant gives access to highly strained molecules containing small rings, as has been demonstrated by irradiation of norborn-5-ene-2-one 10 ... 

Use is made of the Francis formula (equation 6.43). where, as in the previous example, n — 0. In the context of this example the height of liquid flowing over the weir is usually designated hmv and the volumetric liquid flow by Q. Rearrangement of equation 6.43 gives ... 

An experimental probe for the presence of radical intermediates resulting from thermally induced homolytic cleavage of the N-0 bond was derived by incorporating an alkene into a model substrate to act as a potential intramolecular radical trap (Scheme 6.25) [11]. In a control experimental, thermal reaction of 73 gave the desired product 74 in 66% isolated yield. On the other hand, thermal rearrangement of the unsaturated compound 75 under our typical conditions gave the desired hydroxypyrimidinone 76 in only 38% isolated yield. When the vinyl ami-doxime mixture 75Z/E was heated in o-xylene at 125 °C in the presence of a... 

We note that n in the summand of Eq. (20) annuls terms with n = 0 and permits the sum to start with n > 1. Thus, Eq. (20) can be rearranged to have an explicit leading factor of zi. This colligative property was noted above. Of course, a determination of Z establishes the solute chemical potential //1 we seek. We are motivated, therefore, to examine the coefficient multiplying zi. To that end, we bring forward the explicit extra factor in zj and rearrange Eq. (20) to obtain... 

For the first time, the primary nitrone (formaldonitrone) generation and the comparative quantum chemical analysis of its relative stability by comparison with isomers (formaldoxime, nitrosomethane and oxaziridine) has been described (357). Both, experimental and theoretical data clearly show that the formal-donitrones, formed in the course of collision by electronic transfer, can hardly be molecularly isomerized into other [C,H3,N,0] molecules. Methods of quantum chemistry and molecular dynamics have made it possible to study the reactions of nitrone rearrangement into amides through the formation of oxaziridines (358). 

It was demonstrated that treatment of nitronate Me02CH=N(0)0Me with HCI (246), as well as heating (298) affords oxime (104a) as a result of standard thermal decomposition of alkyl nitronates, which occurs via a Cope rearrangement (233) (Scheme 3.87). 

For acyl nitronates of the general formula RCH=N(0)OAc, two types of rearrangements were suggested (Scheme 3.102), which are associated, respectively, with 1,2-migrations of the N-oxide oxygen atom (223) or the OAc fragment (219). 

Six-membered cyclic nitronates can undergo rearrangements accompanied by cleavage of the endocyclic N-0 bond or by cleavage of the endocyclic C-0 bond. The latter fact is evidently associated with the presence of substituents, which efficiently stabilize the positive charge, at the C-6 atom. This occurs upon treatment of nitronates (154a,b) with silicon dioxide (Scheme 3.123) (117). 

The presence of the bond in the trans-antiparallel position with respect to the cleaved N-0 bond allows concerted 1,2-migration (a diotropic process). Apparently, the result of these rearrangements is also determined by the fact that the pseudo-axial position is substantially more favorable for the 0-2 atom in nitroso acetals (243). 

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