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)
URI
http://erepository.uonbi.ac.ke:8080/xmlui/handle/123456789/32716http://www.ncbi.nlm.nih.gov/pubmed/22849426
Citation
J Org Chem. 2012 Sep 7;77(17):7411-27. doi: 10.1021/jo301232w. Epub 2012 Aug 16Publisher
Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA