Rosendo Hernández

Intramolecular hydrogen abstraction. Iodosobenzene diacetate, an efficient and convenient reagent for alkoxy radical generation

Photolysis of several hydroxy compounds in presence of iodosobenzene diacetate and iodine leads to alkoxy radical derivatives which undergo intramolecular hydrogen abstraction to produce cyclic ethers in good yield.

Synthesis of 1,4-epimine compounds. Iodosobenzene diacetate, an efficient reagent for neutral nitrogen radical generation

Abstract Photolysis of several nitroamines, cianamines, and phosphoroamidates in the presence of iodosobenzene diacetate (IBDA) and iodine leads to neutral aminyl radicals which undergo intramolecular hydrogen abstraction to produce epimine compounds with yields that are favorably compared with those obtained with the system lead tetraacetate and iodine.

Intramolecular hydrogen abstraction. Hypervalent organoiodine compounds, convenient reagents for alkoxyl radical generation

The photolyses of 5α-cholestane-3β,6β-diol 3-acetate (1), 5α-cholestan-2β-ol (4), 5α-cholestan-4β-ol (8), (20R)-pregn-5-ene-3β,20-diol 3-acetate (19), (20S)-pregn-5-ene-3β,20-diol 3-acetate (21), and dihydrotigogenin 3-acetate (25) in the presence of iodine and various hypervalent organoiodine compounds lead to alkoxyl radicals which undergo intramolecular hydrogen abstraction to produce, in most cases, 1,4-iodohydrins and tetrahydrofuran derivatives.

Steroidal N-nitroamines. Part 4. Intramolecular functionalization of N-nitroamine radicals: synthesis of 1,4-nitroimine compounds

Photolysis of 6β-nitroamino-5α-cholestane (4), 6β-nitroamino-5α-cholestan-3β-yl-acetate (5), 2β-nitroamino-5α-cholestane (13), 4β-nitroamino-5α-cholestane (17), (20R)-20-nitroaminopregn-5-en-3β-yl acetate (26), (20R)-(31) and (20S)-(34)-nitroamino-5α-pregnan-3β-yl acetate, (23R, 25S)-3β-acetoxy-23-nitroamino-5β-spirostan (46), 3β-nitroaminofriedelane (53), and methyl 3β-nitroaminofriedelan-29-oate (54) in the presence of iodine and various oxidative reagents leads to neutral nitroaminyl radicals which undergo intramolecular hydrogen-abstraction to produce in most cases N-nitroimine compounds. Best results were obtained with the system iodine and (diacetoxyiodo) benzene.

Catalytic, One-Pot Synthesis of β-Amino Acids from α-Amino Acids. Preparation of (α,β-Peptide Derivatives

The one-pot conversion of readily available alpha-amino acid into beta-amino acid derivatives was carried out in good yields. The method is a sequential process initiated by a tandem radical decarboxylation-oxidation reaction; the resulting acyliminium ion was trapped by silyl ketenes. Stoichiometric and catalytic versions of this reaction were developed and then applied to prepare modified di- and tripeptides. Interestingly, some tripeptides formed expanded beta-turns in the solid state.

Long-acting contraceptive agents: testosterone esters of unsaturated acids

The synthesis of 13 new esters of testosterone is described, with the esterifying acids bearing acetylenic, olefinic, or polyunsaturated functions in the chain, for evaluation as long-acting androgens.

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.

Synthesis of alkaloids from amino acids via N-acyliminium ions generated by one-pot radical decarboxylation–oxidation

Abstract A one-pot methodology for the synthesis of α-substituted nitrogen heterocycles from commercial amino acids has been developed. Good stereoselectivity can be achieved with chiral substituted rings. This procedure has been applied to the synthesis of piperidine, pyrrolidine and indolizidinone alkaloids.

Labdane diterpenes from Cistus symphytifolius

Abstract The investigation of the aerial part of Cistus symphytifolius afforded, in addition to sitosterol, trimethoxykaempferol, cativic acid, labdenic acid, labdanolic acid and labdan-8α,15-diol, three new bicyclic diterpenes: cistadienic acid, cistenolic acid and labd-13( E )- ene-8α,15-diol. The structures of these were determined by spectral studies and correlations. CD spectral studies showed that cistenolic acid and salvic acid are enantiomeric compounds, so the stereochemistry of salvic acid (7α-hydroxy-labd-8(17)-ene-15-oic acid) should be changed to 7β-hydroxy-eperu-8(17)-ene-15-oic acid (7β-hydroxy- ent -labd-8(17)-ene-15-oic acid).

Fragmentation of alkoxy radicals: Mechanistic aspects of the tandemβ-fragmentation-intramolecular functionalization reaction

Abstract The formation of the β-peroxylactone (4) during the photolysis of lactol (3) with (diacetoxyiodo)-benzene (DIB) and iodine under oxygen atmosphere demostrates the presence of a peroxyradical intermediate in the tandem β-fragmentation-intramolecular functionalization reaction.