N-Benzylmorpholine, -piperidine, and -pyrrolidine (1A-C, resp.) are oxidised by RuO4 (generated m situ) at both endocyclic and exocyclic (benzylic) N-c~ methylene positions to afford lactams (and dioxo-derivatives) and benzaldehyde (and benzoyl derivatives), respectively. The N-oxides of 1A-C, formed by a minor side reaction, are not involved as intermediates. Control experiments showed the transient formation of endo-and exocyclic iminium cations trapped with NaCN as the corresponding nitriles. The proposed course of the RuO4-mediated oxidation of 1A-C involves the consecutive steps 1 a iminium cations + cyclic enamine ~ oxidation products. The endocyclic/exocyclic regioselectivity of the oxidation reaction lies between 0.8 (for 1A) and 2.1 (for 1B). The amine cation radical and the N-c~-C. carbon centered radical seem not to be involved. 9 Central European Science Journals. All rights reserved.

From the determination of product composition and overall second-order rate constants for the reactions of a number of cyclic quaternary ammonium ions with sodium methoxide in methanol and previous similar data, a complete set of partial rate coefficients for the ring-opening reactions (substitution and elimination) of 1,l-dimethyl cyclic ammonium ions and their a,&-dimethyl-substituted derivatives for ring sizes 4-6 was made available. Such reactions are sensitive probes for steric strain and reaction mechanism requirements in the @-elimination reaction and for the different stereochemical requirements of elimination vs. substitution.Ring opening of cyclic quaternary ammonium ions under the action of anionic reagents may occur by either substitution or elimination. In the preceding paper' we have reported that the ring-opening reactivity of such substrates appears to be affected by two major factors, i.e., the ring strain and the geometrical requirements of the reaction. The role of the latter factor was made apparent by the fact that the five-membered ring is more reactive in the ringopening substitution reaction and less reactive in the ring-opening elimination reaction than expected from ring strain effects. If methyl groups are present a t the a positions of the heterocyclic ring, a @-hydrogen is expected

1,4-Dibenzylpiperazine (1), -2-piperazinone (7), -2,6-piperazinedione (9), and 1-benzoyl-4-benzylpiperazine (30) were oxidized by RuO 4 (generated in situ) by attack at their endocyclic and exocyclic (i.e., benzylic) aminic N -α-C-H bonds to afford various oxygenated derivatives, including acyclic diformamides, benzaldehyde, and benzoic acid. The reaction outcome was complicated by (i) the hydrolysis of diformamides, occurred during the work-up, and (ii) the reaction of benzaldehyde with the hydrolysis-derived amines giving imidazolidines and/or Schiff bases. Benzoic acid resulted from benzaldehyde only. Compounds 7, 30, and 1-benzylpiperazine, but not 9, were transiently formed during the oxidation of 1. In the same reaction conditions, 1,4-dibenzyl-2,3-(or 2,5)-piperazinedione, 1,4-dibenzyl-2,3,6-piperazinetrione, 4-benzoyl-1-benzyl-2-piperazinone, and 1,4-dibenzoylpiperazine were inert. The proposed oxidation mechanism involves the formation of endocyclic and exocyclic iminium cations, as well as of cyclic enamines. The latter intermediates probably result by base-induced deprotonation of the iminium cations, provided an N + −β-proton is available. In the case of 1, the cations were trapped with NaCN as the corresponding α-aminonitriles. The statistically corrected regioselectivity (endocyclic/exocyclic) of the RuO 4 -induced oxidation reaction of 1, 7, and 30 was 1.2-1.3.

Following a suggestion by the late Lennart Eberson, we have employed the ICl-HFP (HFP being hexafluoropropan-2-ol) system in iodination reactions, and found unambiguous evidence for the occurrence of an ET-mechanism of halogenation. The evidence is based on the use of 'intelligent' substrates, which make it possible to fix the boundaries between the occurrence of an ET-mechanism and of a conventional polar mechanism. In an 'intelligent' substrate, in fact, the nature of the product(s) changes significantly depending on the operating mechanism. The ICl-HFP combination is instrumental to the onset of a one-electron oxidation with electron-rich substrates, followed by halogenation. The most prominent example is that of the electron-rich substrate durene (1,2,4,5-tetramethylbenzene, DUR), when compared to mesitylene (1,3,5-trimethylbenzene, MES): with a 'conventional' iodination system (i.e., I 2 / Ag ϩ ) and in common solvents, where the polar mechanism holds, durene is less reactive (k MES /k DUR = 46 ± 3), but becomes more reactive (k MES /k DUR = 0.23) in HFP with ICl, where the ET-mechanism takes over. Other substrates also support the onset of ET-pathways in HFP. Finally, a preliminary survey of a biohalogenation reaction induced by laccase indicates the modest occurrence of a polar process of iodination with a few substrates.

Excess N‐benzyl aziridine (1) reacts with I2 to afford dimer 2, tetramer 3, benzaldehyde (4), and iodoamine 5. The reaction is interpreted as occurring by both electron transfer (ET) and heterolytic mechanisms. An ET mechanism is substantiated for the oxidation by I2 of dimer 2 and tetramer 3, both being substrates easier to oxidise by electron abstraction than 1. Several auxiliary reactions were performed on 1 in order to firmly establish the boundaries to the competition between the ET and heterolytic mechanisms. For the reaction of 1 with 5 a reaction scheme is proposed; in a particular case, a pseudo‐first order kinetic law is followed.