Francisco Yuste

Selective reduction of aromatic nitro compounds containing o- and n-benzyl groups with hydrazine and raney nickel

Abstract The selectiity in the catalytic reduction of aromatic nitro compounds containing O-benzyl, N-benzyl or chlorine with hydrazine and Raney nickel was studied.

Asymmetric Diels-Alder reactions of γ-alkoxy-α-sulfinylbutenolides

Abstract The synthesis of the enantiomerically pure 5-ethoxy-3- p -tolylsulfinyl-2(5H)-furanones ( 2a and 2b ) and the study of their behaviour as dienophiles in asymmetric Diels-Alder reactions with cyclopentadiene are reported. Depending on the reaction conditions, the π-facial selectivity is mainly controlled by the sulfur or C-5 configurations.

Asymmetric Synthesis of (S)-(−)-Xylopinine. Use of the Sulfinyl Group as an Ipso Director in Aromatic SE

Optically pure (S)-(-)-xylopinine 2 was prepared in three steps in 52% overall yield. Thus, condensation of the carbanion derived from (S)-4 with the (S)-(E)-sulfinylimine 5 gave a 2:1 mixture of tetrahydroisoquinolines 6a and 6b, differing only in configuration at sulfur. N-Desulfinylation of this mixture gave the diastereomeric sulfoxides which, without separation, were converted into (S)-(-)-xylopinine (2) with loss of the sulfinyl moieties under Pictet-Spengler conditions. This unprecedented ipso electrophilic substitution of a sulfinyl group may have synthetic implications beyond that described in this work.

Synthesis of enantiomerically pure 2-amino alcohols from amino acids mediated by sulfoxides

Abstract Enantiomerically pure (R1,S2)- and (S1,S2)-2-amino alcohols can be easily synthesized by stereodivergent reduction of α′-(N-Boc)amino β-keto sulfoxides (easily synthesized from readily available N-Boc amino ester hydrochlorides) with DIBAH (de 82–92%) and DIBAH/ZnBr2 (de 80%), followed by hydrogenolysis of the C–S bond of the resulting hydroxy sulfoxides and final hydrolysis of the N-Boc protecting group.

Asymmetric synthesis of α-acetylenic epoxides

Abstract Chiral α-acetylenic oxiranes were easily synthesized from readily available propargylic esters by a four-step sequence involving the stereoselective reduction of α′-alkynyl β-keto sulfoxides with DIBAH (de 66–78%) and DIBAH/ZnBr2 (de 78–88%), followed by further reduction of the resulting hydroxy sulfoxides into the corresponding sulfenyl derivatives and final epoxy ring closure via sulfonium salt.

Methyl Sulfinates as Electrophiles in Friedel–Crafts Reactions. Synthesis of Aryl Sulfoxides

The Friedel-Crafts reaction of methyl alkyl- and arylsulfinates with aromatic systems, activated by one or more electron-donating substituents (OH, OMe, NHR, NR(2)), provides alkyl aryl and diaryl sulfoxides under mild conditions and in moderate to good yields. The very high regioselectivity usually observed in these sulfinylation reactions is rationalized on the basis of a Wheland intermediate having a trigonal bypyramidal structure in which steric and electronic interactions are significant factors strongly destabilizing the attack to the ortho positions.

Isomerization of Perezone into Isoperezone and Preparation of Dihydroisoperezinone

Abstract The reaction of perezone 1 with 3,4,5,6-tetrahydro-2-pyrimidinethiol 11 promotes a 1,2-carbonyl transposition in the quinoid ring of 1 giving rise to isoperezone 8, which treated with BF3·Et2O produces dihydroisoperezinone 9.

1,3-Dipolar Cycloaddition of Diazoalkanes to (S)-(+)-3-[(4-Methylphenyl)sulfinyl]-5,6-dihydropyran-2-one. Synthesis of Optically Pure Cyclopropanes by Denitrogenation of Sulfinyl and Sulfonyl Pyrazolines

The addition of diazomethane and diazoethane to enantiopure (S)-(+)-3-[(4-methylphenyl)sulfinyl]-5,6-dihydropyran-2-one (3) afforded the corresponding pyrazolines 4 and 6-exo in good yields and with almost complete pi-facial selectivity. When the reaction is effected in the presence of Yb(OTf)(3), the facial selectivity is inverted to give the pyrazolines 5 and 7-exo. The denitrogenation of optically pure sulfinyl pyrazolines 4-7-exo into the corresponding cyclopropanes with Yb(OTf)(3) occurred with complete retention of configuration but moderate chemoselectivity and yields. These results were significantly improved starting from sulfonyl pyrazolines, which afforded optically pure 3-oxabicyclo[4.1.0]heptan-2-ones with yields ranging between 65% (17 and ent-17) and > or = 95% (16 and ent-16).

A stereodivergent approach to syn- and anti-β-hydroxy-γ-amino acids. Enantioselective synthesis of N-Boc-statine and N-Boc-3-epistatine mediated by sulfoxides

Abstract Asymmetric syntheses of the syn- and anti-stereoisomers of N-Boc statine, based on the stereodivergent reduction of a single sulfoxide 5, derived from N-Boc- l -leucine, are reported.

Synthesis and dienophilic behavior of enantiomerically pure (E)-2-p-tolylsulfinylacrylonitrile derivatives

Abstract The synthesis of (E)-3-formyl 2-sulfinylacrylonitrile 2 and its diethylacetal derivative 3, as well as their behavior as dienophiles in reactions with cyclopentadiene are reported. The acetal 3 evolved with high π-facial selectivity under Eu(fod)3 catalysis. The π-facial selectivity became almost complete after extended reaction times, which evidences that a retro Diels–Alder reaction occurs. The endo/exo selectivity (ca. 80:20) was only moderate. The reactivity of the aldehyde 2 was higher but its evolution was less stereoselective than that of 3, the endo/exo product ratio observed being close to 1.