Carmen Betancor

Three triterpenes and other terpenoids from Catha cassinoides.

Abstract The investigation of stems and leaves of Catha cassinoides afforded, in addition to sitosterol, β-amyrin, ursolic acid, lup-20(29)-en-3β,30-diol and friedelin, three new pentacyclic triterpenes: 30-hydroxyfriedelan-3-one, 29-hydroxyfriedelan-3-one and 3-oxo-friedelan-29-oic acid. The structures ofthese were determined by spectral studies and correlations, and were confirmed by X-ray analysis of 29-hydroxyfriedelan-3-one acetate.

Intramolecular functionalization of N-cyanamide radicals: synthesis of 1,4-and 1,5-N-cyanoepimino compounds

Photolysis of 3β-methoxymethoxy-5α-cholestan-6β-ylcyanamide (6), 29-methoxyfriedelan-3β-yl-cyanamide (15), (22R,25R)-5α-furostan-26-ylcyanamide (23), 8α,12-(12R/12S)-epoxylabdan-15-ylcyanamides, (32) and (33), in the presence of iodine and lead tetra-acetate leads to neutral cyanimyl radicals which undergo intramolecular hydrogen abstraction to produce N-cyanoepimino compounds. Better results are obtained with the system iodine and diacetoxyiodobenzene. The starting cyanamides have been prepared by reduction of the oximes (3) and (13) and of the amides (20), (28), and (29), respectively, with lithium aluminium hydride followed by cyanation with cyanogen bromide or with sodium cyanate and subsequent dehydration of the urea derivative with methanesulphonyl chloride.

Fragmentation of alkoxy radicals : tandem β-fragmentation-cycloperoxyiodination reaction

Abstract A new tandem β-fragmentation-cycloperoxyiodination reaction is observed when a homoallylic alcohol is irradiated with visible light in the presence of (diacetoxyiodo)benzene and iodine under an atmosphere of oxygen. A synthetically interesting epidioxyiodide medium-sized ketone is obtained by this method.

Sequential alkoxy radical fragmentation-cyclopropylcarbinyl rearrangement. Synthesis of highly functionalized eleven-membered rings

The steroidal 5α-alcohol (3) with (diacetoxyiodo)-benzene and iodine under irradiation with visible light undergoes a tandem alkoxy radical β-fragmentation-cyclopropylcarbinyl rearrangement reaction to give the eleven-membered cyclic ketone (4). Under oxygen pressure peroxidation of the C-radical intermediate takes place to afford the highly functionalized eleven-membered cyclic ketone (6) in moderate yield.

Triphenylbismuth dibromide-iodine: An efficient reagent for the dehydration of alcohols

Abstract Tertiary and secondary alcohols react under mild conditions with triphenylbismuth dibromide and iodine under an inert atmosphere to give the corresponding most stable alkenes in good yields.

Sequential alkoxy radical fragmentation. A one-step method for breaking two 1,3-positioned CC bonds

Abstract Cyclic hydroxy-ketones (bd1) and (bd2) in the presence of (diacetoxyiodo) benzene or mercuric oxide and iodine under oxygen atmosphere and irradiation with visible light undergo a new sequential alkoxy radical fragmentation-radical peroxidation-peroxyradical cyclization-alkoxy radical fragmentation reacton. This methodology allows the cleavage of two 1,3-positioned CC bonds in a single step and constitutes a new synthesis of β-peroxylactones.

The reaction of enols with superoxide anion radicals: preparation of tertiary α-ketols

Pregnan-20-ones (1) and (4), and 3β-hydroxy-5α-cholestan-6-one (7) react with KO2 and 18-crown-6 in benzene solution and under an oxygen atmosphere at 6–7 °C to give the corresponding α-hydroperoxides (2), (5), and (8) which after treatment with Ph3P gives α-ketols (3), (6), and (9) in good yields.

Hypervalent iodine reagents: Synthesis of a steroidal orthoacetate by a radical reaction

Abstract The reaction of steroidal alcohols ( 1 ) and ( 8 ) with (diacetoxyiodo)benzene and iodine under irradiation with visible light afforded, in addition to the expected β-fragmentation diene ( 2 ), the orthoacetate ( 4 ) in moderate yield.

2-Oxazolines (4,5-dihdro-oxazoles) by organoselenium-induced cyclisation of allylic ureas

The reaction of allylic ureas with phenylselenenyl chloride in the presence of silica gel affords 2-oxazolines in good to excellent yields; 2-oxazolines are also stereospecifically obtained from β-phenylseleno ureas by chemoselective alkylation of the selenium atom followed by basic treatment.

Regioselectivity of the reaction of 3-keto steroids with potassium superoxide

The regioselectivity in the oxidation of different types of 3-keto steroids with potassium superoxide in the presence of 18-crown-6 has been investigated. In all cases, the reaction products are directly related to the enolization process of the substrates. The oxidation of a 2-enolate results in oxidative cleavage of ring A with loss of carbon monoxide to give the lactols (2) and (10) and the aldehyde (8). However, the oxidation of 4-enolates occurs with oxidative cleavage of ring A to give the ketones (7) and (12), the latter with loss of carbon monoxide.