Živorad Čeković

Reactions with lead tetraacetate—IV : Oxidation of saturated aliphatic alcohols—II; Alcohols of low molecular weight

Abstract The action of lead tetraacetate on ethanol, 1-propanol, 2-propanol and 2-butanol has been studied under various experimental conditions, and it was found that the tetravalent lead compound reacts with alcohols in ways not so far observed. The possible reaction schemes are discussed in terms of homolytic and heterolytic cleavage of the intermediate alkoxy lead acetate complexes.

Assignment of cis-trans configuration to constitutionally symmetrical 2,5-dialkyl-tetrahydrofurans

Abstract The configurations previously assigned to the cis-trans stereoisomers of 2,5-dimethyl-tetrahydrofuran and 2,5-diethyltetrahydrofuran have been established by synthesis, involving the lead tetraacetate oxidation of the corresponding, optically active secondary aliphatic alcohols.

The reaction of lead tetraacetate with alicyclic alcohols—I cycloalkanols☆☆☆

Abstract Secondary cycloalkanols, containing 4- to 16-membered rings, have been treated with lead tetraacetate in refluxing benzene. It was found that the ease of oxidation to the corresponding ketones follows the reactivity order of reactions of alicyclic compounds involving an sp3 → sp2 ring carbon hybridization change, and that the amount of β-fragmentation resulting in opening of the ring is in accord with the total strain associated with carbocyclic rings. The yield of intramolecular ether formation appears to depend upon ring size and conformational factors in the transition state; it increases from cyclohexanol to cyclooctanol, drops sharply for cyclododecanol and reaches the highest value with cyclohexadecanol. The major ether obtained in the case of cyclodecanol was trans-1,2-epoxycyclodecane.

Radical cyclization reactions. Cyclopropane ring formation by 3-exo-cyclization of 5-phenylthio-3-pentenyl radicals

Abstract Free radical cyclopropane ring closure was accomplished by thermal decomposition of thiohydroxamic esters of 6-phenylthio-4-hexencic acids. When the reaction was performed in the presence of acrylonitrile; an addition/cyclization/elimination process took place and the corresponding cyclopentanecarbonitriles were obtained.

Free radical alkylation of the remote nonactivated δ-carbon atom

Abstract A free radical introduction of functionalized alkyl chains into the δ-carbon atom (Michael type alkylation) of alkyl nitrites and alkyl benzenesulfenic-O-esters was achieved.

Free radical annulation of cyclopentane ring

Abstract Homoallyl radical, e.g. 2 , reacts with an electron-deficient olefinic bond 1 with a new CC bond forming and arising of a 5-hexenyl radical 3 which further undergoes to 5-exo-trigonal cyclization with a cyclopentane ring ( 4 ) annulation.

Alkylation of remote non-activated δ-carbon atoms: Addition of δ-carbon radicals, generated by 1,5-hydrogen transfer in alkoxy radical intermediates, to activated olefins

Abstract A free radical introduction of a functionalized alkyl chain onto remote non-activated δ-carbon atoms (Michael type alkylation) has been achieved. Photolysis of suitable alkyl nitrites involves generation of δ-alkyl radicals and in the presence of radicophilic olefins, intermolecular addition takes place and affords δ-alkylated products in 36–80% yields. δ-Alkylation is also achieved in the reaction of alkyl benzenesulfenates with tributyltin hydride (TBTH), in the presence of activated olefins and introduction of a functionalized alkyl chain involves alkoxy and δ-carbon radicals. Products with functionalized alkyl chains were obtained in 36–86% yields. δ-Alkylation of alkyl benzenesulfenates also occurs in the reaction with hexabutylditin in the presence of activated olefins.

Lead tetra-acetate oxidation of saturated aliphatic alcohols—V : Factors influencing the formation of cyclic ethers and carbonyl compounds☆☆☆

Abstract Factors influencing the relative rates of the homolytic and heterolytic processes in the lead tetra-acetate oxidation of unbranched primary and secondary aliphatic alcohols have been investigated, with a view to determine the conditions giving optimal yields of cyclic ethers or carbonyl compounds.

Intermolecular free radical additions to strained cycloalkenes. Cyclopropene and cyclobutene as radical acceptors

Abstract Intermolecular additions of electrophilic radicals to cyclopropene and cyclobutene derivatives afford the addition products in 37–50% yield. The strain relief in the intermediary radical accelerates the addition, as shown by competitive addition experiments.

Free radical phenylthio group transfer to nonactivated δ-carbon atom in the photolysis reactions of alkyl benzenesulfenates

Abstract A free radical phenylthio group transfer from oxygen to the non-activated δ-carbon atom was achieved by irradiation of alkyl benzenesulfenates 1 in the presence of hexabutylditin, and δ-phenylthio alcohols 2 were obtained in 35–91% yields. However, when reactions were performed in the presence of activated olefins an alkylation of δ-carbon occured and phenylthio ethers of type 3 were obtained modest yields.