title: Synthetic studies on furanosteroids: construction of the viridin core structure via Diels-Alder/retro-Diels-Alder and vinylogous Mukaiyama aldol-type reaction.
abstract: 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 (R(1) = 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).
authors: Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
authors: Evans O
authors: EO
authors: Onyango
authors: Peter A
authors: PA
authors: Jacobi
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D000736:Androstenes / Q000737:chemistry*; D001430:Bacteriocins / Q000737:chemistry*; D005663:Furans / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism; D013256:Steroids / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000447:Aldehydes; D000736:Androstenes; D001430:Bacteriocins; D005663:Furans; D013256:Steroids; C116609:3-hydroxybutanal; C012097:viridin