John L. Courtneidge

5—Endo ring closures of allylic hydroperoxides: Useful routes to 1,2—dioxolanes involving strongly stereoselective free radical and polar reactions

Abstract Intramolecular cyclisation of simple allylic hydroperoxides to give substituted 1,2—dioxolanes using electrophilic reagents has been investigated. Closure using mercury(II) acetate and electrophilic halogen reagents (NBS, Br 2 Bu t OC1) occurs by Markovnikov—directed and conformationally strict stereospecificity. Subsequent free— radical reaction of the mercurated dioxolanes involved specific reaction involving reaction from the sterically unprotected face of the intermediate dioxolanyl radical.

Rate constants for the formation of oxiranes by γ-scission in secondary β-t-butylperoxyalkyl radicals

Rate constants for the title reactions have been determined from the ratios of oxirane to peroxide obtained in the reductions of β-bromoalkyl t-butyl peroxides with tributyltin hydride. At ca. 298 K the rate constants are 0.32, 1.12, 1.96, 2.0, and 6.2 × 106 s–1 for β-t-butylperoxy derivatives of trinorbornan-2-yl (exo) cyclohexyl, 1-methylpropyl, cyclopentyl, and 1-ethylbutyl, respectively. The results are discussed in terms of steric and electronic effects in the transition state leading to ring closure of the radicals.

An ESR study of the mercuration of the biphenylene radical cation. Evidence for a homolytic mechanism of mercuration

Abstract When a solution of biphenylene in trifluoroacetic acid containing mercury(II) trifluoroacetate is photolysed with ultraviolet light, the ESR spectra show the progressive mercuration of the biphenylene radical cation in the β-position. β-Proton hyperfine coupling [a(Hβ) 3.58 G] is lost, and 199Hg primary, secondary, and tertiary satellites [a(199Hgβ) 76–77 G] appear untl tetra-β-mercuration is complete. It is concluded that, apart from the usual electrophilic mechanism, an alternative mechanism for mercuration exists, and that this probably involves collapse of the aromatic radical cation, ArH+., with its counterion, HgX2-.: ArH + HgX2 → ArH+. + HgX2 → HAr H − X2 → ArHgX + HX

The nature of the counterion in butyllithium/potassium t-alkoxide reaction mixtures: An ESR study

Abstract The ESR spectrum of the cycloheptatrienyl radical dianion, which is in equilibrium with the corresponding trianion generated by the reaction of cycloheptene with a 1/1 n-butyllithium/potassium tamyloxide mixture, is characteristic of the potassium rather than the lithium salt.

The E.S.R. spectrum of the tetra(1-adamantyl)cyclobutadiene radical cation

Abstract A revised interpretation is proposed for the 1H and 13C hyperfine coupling in the e.s.r. spectrum of the tetra-1-adamantylcyclobutadiene radical cation, and assumes that free rotation occurs about the 1-adamantyl bond.

Alkoxyl radicals from alcohols I. The hypoiodite reaction of cyclopentanol: evidence for sequential rather than competitive reaction pathways

Abstract The representative photostimulated hypoiodite reaction of cyclopentanol with mercury(II) oxide and iodien gives products formed by a sequence of iodoaldehyde formation, followed by consumption to give Baeyer-Villiger and hydrolysis products.

Initiated, tert-butyl hydroperoxide-loaded, low-temperature autoxidation of alkenes: a chemoselective synthesis of allylic hydroperoxides, allowing analysis of the regioselectivity of hydrogen atom abstraction from some unsymmetrically substituted substrates

A method for the preparation of allylic hydroperoxides is introduced: the method involves the rapid, low-temperature, initiated autoxidation of an alkene (in these instances 1-methylcyclohexene and the isomeric 4-methyloct-4-enes) in the presence of tert-butyl hydroperoxide. The success of the method relies upon the selectivity of hydrogen atom abstraction from the substrate by the chain-carrying tert-butylperoxyl radicals, according to the preference for formation of the most stable intermediate allylic radicals, and the reduced rates of chain termination via these same radicals. The method gives a regioselectivity for attack broadly in agreement with predictions from Bollands rules, and a sufficiently high chemoselectivity for allylic hydroperoxide formation that ready isolation of these products in good yield is achieved.

Preparation of unsaturated hydroperoxides from N-alkenyl-N'-p-tosylhydrazines

Unsaturated hydroperoxides (R1R2CHO2H), 2-phenylpent-4-enyl hydroperoxide (1), 3-phenylhex-5-en-2-yl hydroperoxide (2), 5-methylhex-5-en-2-yl hydroperoxide (3), cyclo-oct-4-enyl hydroperoxide (18), and cyclo-oct-3-enyl hydroperoxide (24) have each been prepared from the corresponding carbonyl compound (R1R2CO) by the sequence: i, conversion to the p-tosylhydrazone (R1R2CN–NHTs); ii, reduction with sodium cyanoborohydride at pH 3.5 to give the N′-p-tosylhydrazine (R1R2CH–NH–NHTs); and iii, oxidation with hydrogen peroxide and sodium peroxide, Isomerisation occurs in the preparation of the cyclo-octenyl hydroperoxides, particuarly if the pH falls markedly below 3.5 in the reduction step.

Initiated tert-butyl hydroperoxide-loaded low-temperature autoxidation of alkenes: alternative hydroperoxide syntheses and the preparation of a complete set of reference materials

A complete set of characterization data for the allylic hydroperoxides prepared from 1-methylcyclohexene and the isomeric 4-methyloct-4-enes is presented. The data relies upon the preparation of allylic hydroperoxides by tert-butyl hydroperoxide-loaded autoxidations, singlet-ene oxidations and nucleo-philic substitution reactions. Appropriate allylic alcohols and relevant scission products have been prepared to support the assignments given.

Carbon–carbon bond scission during the reactions of allylic hydroperoxides with some transition metal compounds. Results relevant to a recent proposal

The proposal that 4-exo closure of an allylic peroxyl radical can account for the titled reactions of pinocarveyl hydroperoxide has been considered in the light of literature data, along with the results of reactions carried out with a range of alternative copper and iron reagents and with the previously examined reagents in the presence or absence of suitable traps: an acid-catalysed pathway is proposed to account for the observed scission reaction.