M.Lj. Mihailović

Configuration and reactivity of ten-membered 5,10-seco-compounds obtained by fragmentation of 5-hydroxy-steroids

Abstract Assignment of configuration to the 1,10-double bond in the cis-trans isomeric 3β-acetoxy-5,10-seco-1,10-cholesten-5-ones has been achieved by means of NMR spectrometry. Some reactions of these new compounds have been studied and, as expected from conformational analysis, it was found that only the trans-isomer readily undergoes transannular cyclizations.

Lead tetraacetate oxidation of saturated aliphatic alcohols.—III : Unbranched primary and secondary alcohols

Abstract The action of lead tetraacetate, in benzene solution, on various unbranched primary and secondary aliphatic alcohols containing 4 to 12 carbon atoms has been investigated and the ratio of carbonyl compounds, cyclic ethers and fragmentation products determined. The results obtained are discussed with regard to the number and length of the n-alkyl rests attached to the carbinol carbon atom of the starting alcohol.

Stereochemistry of cyclic ether formation—II : Intramolecular cyclisation of secondary aliphatic alcohols to tetrahydrofuran-type ethers

Abstract The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb4+, Hg2+, Ag+) salts (AcO)−1, O2−, CO32−-halogen (I2, Br2, Cl2) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described.

A convenient synthesis of 1α- and 1β-hydroxycholesterol

Abstract An efficient procedure for the preparation of 1α-hydroxycholesterol 3-acetate 4 is described, which starts from cholesterol and involves as key steps transannular cyclization of the ten-membered ring ontaining (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one 1 to the oxetane derivative 1α,5-epoxy-5α-cholestan-3β-ol acetate 3, and opening of the four-membered ether ring in the latter compound. 1β-Hydroxycholesterol diacetate 9 was obtained by oxidation of 4 to the 1-oxo derivative 8, followed by metal hydride reduction and acetylation.

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.

Reactions with lead tetraacetate—I : Oxidation of saturated aliphatic alcohols part 1

Abstract When oxidized with lead tetraacetate 1-heptanol and 1-octanol undergo cyclization to give as major products the corresponding 2-alkyltetrahydrofurans, accompanied by a small amount of the isomeric tetrahydropyran derivatives. Secondary aliphatic alcohols, under similar conditions, are converted to a mixture of cis and trans 2,5-dialkyltetrahydrofurans.

Electrochemical cyclization of unsaturated hydroxy compounds. Phenylselenoetherification and phenylselenolactonization

Abstract Phenylselenoetherification and phenylselenolactonization were performed in one step by electrolysis of unsaturated alcohols or carboxylic acids and diphenyl diselenide in organic solvent containing halide ions as mediators.

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.

The reaction of lead tetra-acetate with some acyclic hydroxy-ethers☆☆☆

Abstract By means of lead tetra-acetate in refluxing benzene open-chain 1,2-, 1,3-, 1,4- and 1,5-hydroxy-ethers are mainly converted to the corresponding five-membered or six-membered cylic products. Thus, 2-alkoxy-1-ethanols afford 2-substituted 1,3-dioxolanes in 50–53% yield and 4-ethoxy-1-butanol gives 2-ethoxytetrahydrofuran in 52% yield; 3-alkoxy-1-propanols are oxidized to the corresponding 2-substituted 1,3-dioxans in 26–40% yield and 5-ethoxy-1-pentanol cyclizes to 2-ethoxytetrahydropyran in 46% yield. 2-Phenoxyethanol undergoes ring closure to 1,4-benzodioxan in 15% yield.