A Novel Synthesis of Steroidal Δ4,3,6-Diones Using Pyridinium Chlorochromate (PCC)

Benzyltriphenylphosphonium Peroxodisulfate: A Mild and Inexpensive Reagent for Selective Oxidative Deprotection of Trimethylsilyl and Tetrahydropyranyl Ethers, Ethylene Acetals and Ketals under Non-Aqueous and Aprotic Conditions

Benzyltriphenylphosphonium peroxodisulfate has been found to be an effective reagent for the oxidative deprotection of trimethylsilyl (TMS) and tetrahydropyranyl (THP) ethers, ethylene acetals and ketals to their corresponding carbonyl compounds in excellent yields. Selective oxidative deprotection of TMS ethers in the presence of THP ethers and ethylene acetals (ketals) makes this method a useful and practical procedure in organic synthesis.

Review of chemical syntheses of 7-keto-delta5-sterols

Steroids bearing ketone functionality at carbon-7 are found commonly in nature, and the most prevalent of these are the 7-keto-delta5-sterols. These substances have diverse biological properties and are present in biological samples and food products. For the purpose of studying this class of oxysterols, many chemical methods, involving the chemical oxidation of delta5-sterols to the corresponding 7-keto-delta5-sterol derivatives have been developed to produce these compounds. We have undertaken a review and evaluation of chemical methods for the synthesis of these compounds and have endeavored to enhance one of these procedures to yield products for chemical and biological investigations.

Synthesis of 6-oxy functionalized campest-4-en-3-ones: efficient hydroperoxidation at C-6 of campest-5-en-3-one with molecular oxygen and silica gel

As a reference compound library for the investigation of biosynthesis of brassinosteroids, focused on a pathway from campesterol (1) to campestanol (2), 6-oxy functionalized campest-4-en-3-ones as well as campest-5-en-3-one (7) and campestane-3,6-dione were prepared from 1. Oxidation of 1 with pyridinium chlorochromate buffered by calcium carbonate gave 5-en-3-one (7) in 76% yield. Treatment of 7 with silica gel under an oxygen atmosphere in ethyl ether at room temperature produced efficient hydroperoxidation at the C-6 position to give 6alpha-hydroperoxycampest-4-en-3-one and 6beta-hydroperoxycampest-4-en-3-one in 34% and 49% yields, respectively. These compounds were converted to 6alpha-hydroxycampest-4-en-3-one and 6beta-hydroxycampest-4-en-3-one by reduction with triethyl phosphite. This provided the first example of the practical use of hydroperoxidation at C-6 of a Delta(5(6))-unsaturated 3-oxo-steroid with molecular oxygen and silica gel. On the other hand, oxidation of 1 with pyridinium chlorochromate in the absence of calcium carbonate gave campest-4-ene-3,6-dione in 64% yield. This compound was then converted in a highly stereoselective manner to campestane-3,6-dione with A/B trans ring junction by reduction with titanium (III) chloride in 85% yield.

The Oxidation of Some Steroidal Dienes and Trienes with Chromic Acid

The chromic acid oxidation of steroidal 2,4- and 3,5-dienes and 2,4,6-trienes is shown to take place at the secondary termini of the alkenes rather than at the allylic positions and is rationalized in terms of a sequence of 1:4-additions of chromic acid.

Steroidal 5-en-3-ones, intermediates of the transformation of steroidal 5-en-3 beta-ols to steroidal 4-en-3,6-diones oxidized by pyridinium dichromate and pyridinium chlorochromate

Oxidation of cholesterol (1a) or pregnenolone (1b) with pyridinium dichromate (PDC) in dimethylformamide (DMF) or in dichloromethane (DCM) and pyridinium chlorochromate (PCC) in DCM provided cholest-4-en-3,6-dione (2a) or pregn-4-en-3,6,20-trione (2b). TLC monitoration of the reactions implied that cholest-5-en-3-one (3a) or pregn-5-en-3,20-dione (3b) and cholest-4-en-3-one (4a) or pregn-4-en-3,20-dione (4b) might be intermediates. Individual oxidation of 3a or 3b with PDC and PCC could give 2a or 2b, but 4a or 4b remained unchanged. Further investigation indicated that 4a or 4b was an isomerization product of 3a or 3b on silica gel TLC plate rather than really existence in the reaction mixture. These results shown steroidal 5-en-3-ones were intermediates of the transformation of steroidal 5-en-3 beta-ols to steroidal 4-en-3,6-diones oxidized by PDC and PCC.