Search

Lactols II , obtained by DIBAL reduction of their corresponding lactones I , in equilibrium with their hydroxyaldehyde tautomers III were used in a three-component reductive alkylation with 2-hydroxy-1,4-naphthoquinone to give a series of 3-alkylated 2-hydroxy-1,4-naphthoquinone derivatives IV . [ABSTRACT FROM AUTHOR]

Monofluorinated 3-alkyl-2-hydroxy-1,4-naphthoquinone 4 was prepared in eight steps from commercially available 8-bromooctanoic acid ( 10 ). The key step involved l -proline-catalyzed three-component reductive alkylation (TCRA) of 2-hydroxy-1,4-naphthoquinone ( 5 ) with the optically active aldehyde 7 . [ABSTRACT FROM AUTHOR]

The synthesis of the viridin class of furanosteroids core skeleton from the readily available 2,3-dihydro-4-hydroxyinden-1-one (6) is described. Our strategy was broken down into three parts: (1) Synthesis of functionalized alkyne oxazoles of type 5; (2) intramolecular Diels--Alder/retro-Diels--Alder reaction of 5 followed by tautomerization and elaboration of R to give silylated furanonaphthols 4 bearing an aldehyde side chain; and (3) annulation of ring A by intramolecular vinylogous Mukaiyama aldol-type cyclization. Two major challenges were faced in the last step: (i) furanonaphthol derivatives bearing a β-hydroxyaldehyde functionality (R1 = OH) suffered from dehydration to the E-enal, which is geometrically incapable of cyclization, and (ii) the functionality at C17 had a strong influence on the conversion of 4 to 3, as exemplified by the failure of the free ketone (X = O) or its derivatives (X = H, OH; X = H, OAc) to cyclize. In the end, success was realized with the analogous C17-norketone (X = H, H). [ABSTRACT FROM AUTHOR]