HERON rearrangement

Fig. 22 HF/6-31G optimised geometries and B3LYP/6-31G //HF/6-31G energies (Har-tree) of (a) ground state 78b, (b) transition state 79b, and (c) HERON rearranged product 80b.

Glover, S.A. (2006). HERON rearrangement. In Merck Index (14th edn), Organic Name Reactions ONR-43, O Neil, M.J. (ed.), Merck Co., Inc., Whitehouse Station, NJ. 

A crossover experiment indicated that esters (109) were formed in a concerted HERON rearrangement concomitant with the likely formation of the hydroxynitrene (110) (Scheme 20, pathway (ii)). Joint solvolysis of equimolar quantities of A-acetoxy-A-... 

The fate of A-alkoxy-Af-aminoamides from Af-methylaniline and Af-acyloxy-Af-alkoxy-amides has been modelled at semiempirical, ab initio and density functional levels of theory " . B3LYP/6-31G calculations predicted the HERON rearrangement of the model intermediate 214 to methyl formate (173) and l,l-dunethyldiazene (220) to be exothermic by 5.5 kcalmoG and have an activation energy of 21.4 kcalmoG in the gas phase (Scheme 32). 

Using coupled cluster CCSD(T)//B3P86 methods, the Ea values for HERON rearrangement of model hydrazines 215b-d have also been computed to be between 24 and 34 kcalmoU The authors ruled out alternative concerted rearrangements, which were computed to be energetically unfavourable. 

Other references related to the HERON rearrangement are cited in the literature. ... 

The HERON rearrangement has been studied computationally in conjunction with an experimental study of the decomposition of A,A -diacyl-A,A -dialkoxyhydrazines see Scheme 102. The study has shown that substituent effects are in accord with... 

Aldehyde 54 and the hydroxamic acids 55 were generated together in an acid-catalysed elimination reaction (Scheme 7 pathway (ii)). A crossover experiment indicated that esters are formed in a concerted rearrangement concomitant with the likely formation of the hydroxynitrene 57 (Scheme 7 pathway (iii)) while there is no evidence to date for the formation of hydroxynitrene, joint solvolysis of equimolar quantities of /V-acetoxy-/V-butoxy-/>-chlorobenzamide 26e and N- acetoxy-/V-benzyloxybenzamide 27a afforded significant quantities of butyl p-chlorobenzo-ate (36%) and benzyl benzoate (54%) as the only esters. This is an example of a HERON reaction, which has been identified in these laboratories as a characteristic rearrangement of bisheteroatom-substituted amides.32,33,42 43 155 158 Since ester formation was shown to prevail in neutral or low acid concentrations, it could involve the conjugate anion of the hydroxamic acid (vide infra).158... 

These rearrangement processes are characterised by a transition state in which the alkoxyl group migrates from the amide nitrogen to the carbonyl carbon (Fig. 17a) and therefore involves HEteroatom Rearrangements On Nitrogen the HERON... 

Formation of ester 108 could involve dimerisation of alkoxyamidyls 102 and thermal rearrangement of the hydrazines 107 to esters and nitrogen according to Scheme 12, although a HERON reaction (Scheme 21, pathway (iii)) cannot be discounted under these conditions (vide infra). Anhydrides 101 are almost certainly formed by a HERON reaction (Scheme 21, pathway (ii)). 

Heteroatom rearrangements on nitrogen (HERON) reaction, 67, 70-74, 83, 94 bonding in, 72... 

Where X is a poor leaving group, anomeric destabilization of the NX bond can lead to a novel rearrangement. The HERON (from Heteroatom Rearrangements On Nitrogen) reaction of anomeric amides was discovered in the mid-1990s and involves a concerted... 

The reaction of azide with A-chlorohydroxamic esters has proved to be an excellent source of highly hindered esters . The rearrangement of 82 to 83 (Scheme 16), apart from being highly favourable energetically, is characterized by an early transition state with little disruption to the carbonyl. In these HERON reactions, the N—C 0) bond... 

However, subsequent studies provided unequivocal evidence for consecutive three-centre rearrangements, the first step of which is a normal HERON reaction. Independent studies of decomposition of unsymmetrical hydrazines (227a and 227b) produced esters... 

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