Preparation For AB Ring Synthesis
In the next phase (Scheme 2), starting from ketal 12, the cyclohexane ring was cleaved to provide two anchoring points for fusion with the A ring. Alcohol 12 was protected by a benzyl group. The acetonide protecting group was removed from the ketone. Ketone 14 was converted to silyl enol ether 15 by reaction with trimethylsilyl triflate, and a modified Rubottom oxidation using 3,3-dimethyldioxirane followed by a treatment with camphorsulfonic acid introduced a hydroxyl group alpha to the ketone. Ring opening by oxidative cleavage with lead tetraacetate in methanol gave compound 17. In the next step, the aldehyde was protected as a dimethyl acetal, and the ester was reduced to give primary alcohol 18. The hydroxyl group was converted in a Grieco elimination to the selenide (19), which on oxidation with hydrogen peroxide gave alkene 20. Ozonolysis with ozone and triphenylphosphine provided aldehyde 21.
| Scheme 2 |
|---|
Read more about this topic: Danishefsky Taxol Total Synthesis
Famous quotes containing the words preparation for, preparation, ring and/or synthesis:
“Living each day as a preparation for the next is an exciting way to live. Looking forward to something is much more fun than looking back at something—and much more constructive. If we can prepare ourselves so that we never have to think, “Oh, if I had only known, if I had only been ready,” our lives can really be the great adventure we so passionately want them to be.”
—Hortense Odlum (1892–?)
“With memory set smarting like a reopened wound, a man’s past is not simply a dead history, an outworn preparation of the present: it is not a repented error shaken loose from the life: it is a still quivering part of himself, bringing shudders and bitter flavours and the tinglings of a merited shame.”
—George Eliot [Mary Ann (or Marian)
“Genius resembles a bell; in order to ring it must be suspended into pure air, and when a foreign body touches it, its joyful tone is silenced.”
—Franz Grillparzer (1791–1872)
“It is in this impossibility of attaining to a synthesis of the inner life and the outward that the inferiority of the biographer to the novelist lies. The biographer quite clearly sees Peel, say, seated on his bench while his opponents overwhelm him with perhaps undeserved censure. He sees him motionless, miserable, his head bent on his breast. He asks himself: “What is he thinking?” and he knows nothing.”
—Andre Maurois (1885–1967)