Rocio Medel

Chemoselective protection of thiols versus alcohols and phenols. The Tosvinyl group

Abstract The conjugate addition of aliphatic and aromatic thiols to ethynyl p-tolyl sulphone (tosylacetylene) has been managed to afford Tosvinyl derivatives chemoselectively (in the presence of oxygen nucleophiles) and stereoselectively (isomers Z) in practically quantitative yields. The conditions of choice are: catalytic amounts of Et3N (only 0.5–1.0 mol%), a reaction temperature around 0°C and, for the less acidic thiols, CF3CH2OH or CH3CN/CF3CH2OH as the solvent. Thus, N-Boc-Cys-OMe has been quantitatively protected as its S-Tosvinyl derivative in the presence of N-Boc-Ser-OMe and N-Boc-Tyr-OMe. This novel protecting group is stable to several basic and acidic conditions; its removal is achieved at rt by treatment with an excess of pyrrolidine or at 0°C with alkanethiolate ions.

Reaction of masked o-benzoquinones towards dienophiles with inverse electronic demand. Enol and thioenol ethers as dienophiles

Abstract The Diels-Alder reaction of masked o-benzoquinones and electron-rich dienophiles such as enol ethers and thioenol ethers is described.

One pot michael addition, vinylsulfone isomerization and alkynyl to alkenyl triple bond reduction. Synthesis of a carbasugar related to Rancinamycin III

Abstract Cyclohexenylsufones 2 show a different behaviour in their reactions with Na MeOH system depending on the nature of protecting groups R. In the case of R= TMS, the observed sequence Michael addition-vinylsulfone isomerization-alkynyl to alkenyl reduction has been used for the synthesis of a carbasugar related to the antibiotic Rancinamycin III.

First intermolecular Pauson–Khand reaction of 7-azanorbornenes. Control of the regioselectivity by the effect of the substituents attached to the olefinic partner

Abstract High regioselectivity in the intermolecular Pauson–Khand reaction of 7-azanorborn-5-enes has been found by using 5-bromo-2-endo-tosyl derivatives as the olefinic partner.

Enantioselective synthesis of antibiotic (+)-rancinamycin III derivative and two protected carbasugars of the α-d-talo-series from furan

Abstract The synthesis of (+)- 1 , a carbasugar related to rancinamycin III, has been achieved from diene (+)- 3 in two steps using as the key step the transformation of alkyne (−)- 2 , obtained by resolution of alcohol 6 , into diene (+)- 3 by treatment with Na/MeOH. Moreover, reduction of the carbonyl group in (+)- 1 affords diol (+)- 19 , in which different protection strategies of the hydroxy groups allows one to obtain, selectively, protected derivatives of α- d -carbatalopyranose (+)- 4a and its 6-desoxy derivative (+)- 4b to be obtained selectively.

Enantioselective synthesis of (+)-5,6-exo-(isopropylidendioxy)-2-phenylsulfonyl-7-oxabicyclo[2.2.1]hept-2-ene

Abstract The title compound (+)- 1 has been synthesized in four steps from furan and dienophile (+)- 3 via an asymmetric Diels–Alder reaction.

Synthesis of new 2- or 3-deoxy carbapyranoses from furan

Abstract The synthesis of new 2- or 3-deoxy carbapyranoses of the allo-, galacto-, gluco- and manno-series starting from furan are described.

Remote controlled Haller–Bauer ring opening of bicyclo[2.2.2]octenones

Abstract A new, unprecedented case of the Haller–Bauer reaction in bicyclo[2.2.2]octenones, easily obtained from the Diels–Alder reaction, provides effective and stereocontrolled access to highly substituted cyclohexene derivatives.

Addition of Thiols to Sulfonylacetylenes: Synthetic Applications

The addition of propane-1,3-dithiol to p-toluenesulfonylacetylene affords the dithioacetal 1. This compound is a useful building block for the synthesis of new functionalized sulfanylvinylsulfonyl derivatives.