André Goosen

N-alkoxy-n-acylnitrenium ions in intramolecular aromatic addition reactions

Abstract N-alkoxy-N-acylnitronium ions are generated by treatment of N-alkoxy-N-cohloroamides with silver ions in ethereal solvents. These intermediates readily cyclise onto aromatic nuclei on alkozy side-chains to give benzoxazines and benzoxazepines and on the acyl side-chains to give γ, δ and ϵ benzolactams. Spirane products are formed by ipso addition When a 4-methoxy substituent ia present on the side-chain aromatic rings. The yields and regioselectivities of these reactions have been ascribed to different transition structures for cyclisation onto the acyl and alkoxy side-chains which involve respectively an exocyolic and endocyclic N-0 π-bond. Evidence for this exeptionally high π-bond character has been obtained from MNDO calculations which predict a π-bond order of 0.9 and a rotational barrier of 29.7 kcalmol-1

Synthesis of β=iodo-t-butyl and methyl ethers from the reaction of alkenes with t-butyl and methyl hypoiodites

Abstract t -Butyl or methyl hypoiodite, generated from potassium t-butoxide or sodium methoxide and iodine monochloride, react with olefins via a bridged iodonium ion intermediate giving the trans -vicinal iodo - t -butyl or -methyl ethers.

Factors affecting the electronic states of amidyls: evidence for Π—Σ mixing in simple amidyls

N-Methyl- and N-acetyl-biphenyl-2-carboxamidyls, generated from the corresponding N-bromides in photochemically initiated alkyl radical or bromine atom chain reactions, cyclise to give Ar1-5 and Ar2-6 products, indicating the accessibility of a low-energy excited Σ-state for these species. N-Methoxy-biphenyl-2-carboxamidyl radical, from photolysis of the N-chloro derivative, yields no products from Ar1-5 or Ar2-6 cyclisation; this indicates a thermodynamically stable Π-ground state and a high-energy and thermally inaccessible excited Σ-state. The N-methylbiphenyl-2-sulphonamidyl radical from photolysis of the N-iodo or N-bromo derivative affords only the Ar2-6 product; this represents chemical evidence for a large Π—Σ energy separation. MNDO calculations predict the Π-ground states of N-alkoxy-amidyls and -amiyls to be more nucleophilic than those of amidyls, imidyls, and sulphonamidyls, in keeping with the observed reactivities. The reactivities and regioselectivities observed, together with e.s.r. data and MNDO results, support mixing between the Π-ground and Σ-excited states of amidyls, whereas alkoxyamidyls, cyclic amidyls, and sulphonamidyls have pure Π-ground states. Mixing in amidyls is facilitated by their acyclic nature and by a small energy difference between their Π-ground and Σ-excited states.

Reactions of carbamyl radicals: intramolecular hydrogen abstraction reactions

Abstract ω-Phenylalkyl-N-methylcarbarnyl radicals undergo intermolecular addition to 3,3-dinethylbut-l-ene in preference to intramolecular hydrogen abstraction. Methyl N-(ω-phenylalkyl) carbanyl radicals and methyl N-pentylcarbamyi radicals readily abstract hydrogen through a six membered transition state or a seven membered transition state if the hydrogen is beniylic. The selectivities are interpreted in terms of the electrophilicity of the radical and the stereo-electronic requirements of hydrogen abstraction reactions.

N-alkoxy-N-acylnitrenium ions as possible intermediates in intramolecular aromatic substitution: novel formation of N-acyl-3,4-dihydro-1H-2,1-benzoxazines and N-acyl-4,5-dihydro-1H,3H-2,1-benzoxazepine

N-Halogeno-N-alkoxyamides undergo intramolecular aromatic substitution by thermal- or Lewis acid-catalysed heterolysis of the nitrogen–halogen bond. N-Acyl-N-alkoxynitrenium ions are likely intermediates. N-Chloro-N-methoxybiphenyl-2-carboxamide (4) yields N-methoxyphenanthridone (11) quantitatively with AgBF4, while O-2-phenylethyl-N-chlorobenzohydroxamate (19) is converted in good yield into N-benzoyl-3,4-dihydro-1H-2,1-benzoxazine (21) with AgBF4, AgClO4, HgO, and Hg(OAc)2. N-Acetyl-3,4-dihydro-1H-2,1-benzoxazine (22) is formed similarly. O-3-Phenylpropyl-N-chlorobenzohydroxamate (23) cyclises to N-benzoyl-4,5-dihydro-1H,3H-2,1-benzoxazepine (24) with AgBF4.

Autoxidation of nonane and decane: a product study

The autoxidation of nonane and decane has been shown to occur in three stages. The initial stage leads t o alkyl hydroperoxide formation and in the second stage the hydroperoxide decomposes to produce alcohols and ketones as major products. These studies support the proposal that hydroperoxide decomposition in the second stage occurs by a radical-induced decomposition. In the third stage the products are oxidised in competition with the alkane. Under the conditions of the autoxidation, the alkanes produce γ-lactones as the major ester components and carboxylic acids are formed in the latter stages of the autoxidation. Decan-2-one is shown to be the precursor of heptan-1-01 and octanal.

N-Iodo-amides: mechanism of intramolecular reactions with aromatic rings of amido-radicals in Σ- and Π-electronic states

Intramolecular cyclisations of amido-radicals generated by homolysis of N-iodo-amides onto aromatic systems gives γ- and δ-lactams, in cases where the aromatic rings can rotate, and only δ-lactams in rigid planar systems. Kinetic studies of the cyclisation of N-methylbiphenyl-2-carboxamide with t-butyl hypoiodite under irradiation have shown that γ- and δ-cyclisation products are formed in parallel and that the reactions have different activation energies and entropies. Reactions of N-methyl derivatives of 1,2,3,4-tetrahydro- and 1,2-dihydro-phenanthrene-4-carboxamides with t-butyl hypoiodite under irradiation have provided evidence that Π-conjugation is a prerequisite for δ-lactam formation. From a consideration of the molecular orbitals involved it is suggested that γ- and δ-cyclisation reactions occur with amidyls in the Σ- and Π-electronic states.

N-Iodo-amides: cyclisation of substituted biphenyl-2-carboxamides

Homolysis of N-iodo-amides leads to 2′-, 3′-, and 4′-substituted biphenyl-2-carboxamidyl radicals which cyclise intramolecularly to give γ- and δ-lactams in parallel processes. The proportion of Ar1-5 and Ar2-6 cyclised products is in accord with the steric and electronic effects of the substituents. 4′-Iodo-4′-methoxy-N-methyl-3-oxoisoindoline-1-spiro-1′-cyclohexa-2′,5′-dienes have been identified as spiro-intermediates in the cyclisation of N-methyl-4′-methoxybiphenyl-2-carboxamide.

The mechanism of benzophenone-sensitised oxidation of 9-phenylxanthene with oxygen

From an investigation of the effect of inhibitors, quenchers, and the failure of a singlet sensitiser to effect the oxidation, it is proposed that the benzophenone-sensitised oxidation of 9-phenylxanthene with oxygen is a type I process. Further support for this conclusion is afforded by spectroscopic considerations. Evidence is also presented that the oxidation is a non-chain process, and the effect of acid on the product distribution is discussed.

Reaction of 2-alkyl-2-phenyl-1,3-dioxolans with iodine monochloride: formation of α-phenylalkanoate esters

2-Alkyl-2-phenyl-1,3-dioxolans undergo a high-yield transformation into 2-chloroethyl α-phenylalkanoates upon treatment with iodine monochloride in dichloromethane.