Rubén Gaviño

A mild and efficient method for the chemoselective synthesis of acylals from aromatic aldehydes and their deprotections catalyzed by sulfated zirconia

o C. Ketones and aliphatic aldehydes are found to be unaffected under the reaction conditions. The deprotection of the resulting acylals is achieved using the same catalyst at 60 o C. The catalyst can be reused in two cycles without losing its activity.

Synthesis of a polynorbornene containing 3,5-di-TERT-butyl-4-hydroxybenzoyl group

SummaryA new polynorbornene derivative was synthesized by ring-opening metathesis polymerization (ROMP) of 5- {[(3,5-di-t-butyl-4-hydroxy-benzoyl)oxy]methyl}-2-norbornene (BHBN) using Ru- and Os-based catalysts. The structure and properties of the poly(BHBN) were characterized by NMR, IR, DTA, DSC, and GPC. It was shown that ROMP leads to the formation of high molecular weight polynor-bornene derivatives containing the stabilizing group.

Cyclic and linear oligomerization reaction of 3,4,5-trimethoxybenzyl alcohol with a bentonite-clay

Abstract The catalytic induction and structures of cyclic and linear oligomers from 3,4,5-trimethoxybenzyl alcohol with a bentonite clay as catalyst are discussed.

Polymerization of phenylacetylene with Di-μ-pentafluorothiophenolate bis (1,5-cyclooctadiene) rhodium (I) and its analogues

Abstract Polyphenylacetylene, in good yields and with high molecular weight, has been obtained using three new Rh based catalytic systems, i.e. [Rh(COD)(SC6F5)]2, [Rh(COD)(SC6H5)]2 and Rh(SC6F5)(Pφ3)(COD) where COD = 1,5-cyclooctadiene. 1H- and 13C-NMR spectra have shown that the polyphenylacetylene obtained is highly stereoregular. The dependence of polyphenylacetylene yield and molecular weight on different experimental factors, namely solvent characteristics and monomer initial concentration, is also discussed in this work. Although the mechanism by which these catalysts polymerize phenylacetylene has not been completely elucidated due to its high complexity, new information was obtained and a catalytic mechanism has been proposed.

PYRROLIZIDINE ALKALOIDS FROM SENECIO MULGEDIIFOLIUS, TWO NEW 13-MEMBERED MACROCYCLIC 7,9-DIESTERS

Abstract The structure and absolute configuration of the new 13-membered macrocyclic alkaloids mulgediifoline and oxyretroisosenine were determined on the basis of chemical reactions and conventional spectral studies including differential nOe and 2D NMR techniques, COSY, HETCOR, COLOC, HMBC and NOESY. The absolute stereochemistry of the already known compounds retroisosenine and cis -nemorensic acid was assigned unambiguously.

Aromatic substitution reactions of benzyl derivatives with a bentonite clay

Two examples of catalytic induction with a bentonite clay to form phenylmethanes and aromatic ethers from benzyl derivatives are discussed.

Clerodane diterpenoids from Salvia melissodora

Abstract From two populations of Salvia melissodora Lag., four neo-clerodane diterpenoids were isolated. The structures of these compounds were established by spectroscopic and chemical means. The triterpenoids, oleanolic acid and ursolic acid, together with sitosterol, were also found in this species.

Isocapnell-9-en-8-one and 6α-hydroxyisocapnell-9-en-8-one, sesquiterpenes from Buddleia species☆

Abstract The structure of the new sesquiterpenes, isocapnell-9-en-8-one and 6α-hydroxyisocapnell-9-en-8-one, isolated from two Buddleia species have been elucidated mainly on spectral grounds. The existence of a new carbon skeleton is described.

Neo-clerodane diterpenoids from Salvia madrensis

Abstract From the aerial parts of Salvia madrensis three neo-clerodane diterpenoids: salvimadrensin, salvimadrensinone and salvimadrensinol have been isolated. Their structures were established by spectroscopic means and chemical transformations.

Synthesis of azanucleosides through regioselective ring-opening of epoxides catalyzed by sulphated zirconia under microwave and solvent-free conditions.

New azanucleosides were obtained using sulphated zirconia (ZS) as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl)pyrimidine-2,4(1H,3H)-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl)-pyrimidine-2,4(1H,3H)-dione, with (S)-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.