Multistrategic Retrosynthetic Analysis of Ginkgolide

Such a dissection, which would both remove functionality and lower reactivity, would also reduce the number of stereocenters by four. Simplification of this magnitude is 

Of the two carbocyclic rings in 272 or in simpler precursors such as 275, ring A, which has no independent stereocenters, is more strategic for disconnection. Indeed, ring B and the carbon stereocenter bearing the /-butyl (C-8) qualify for preservation as initial or origin structural units for the synthesis. The stereocenter at C(8) with its bulky 

Among the most logical disconnections of the carbocyclic rings of 272 (or the other precursors shown extending to 278) is that involving the strategic C(4)-C(5), C(6)-0 bond pair in 272 - 278. 

The highest priority ring disconnective T-goals for 272 are those which disconnect a cocyclic 5,5-fusion bond and offexendo bond pair. The internal ketene-olefin cycloaddition in tactical combination with the Baeyer-Villiger transform is well suited to the double disconnection of such a cyclopentane-y-lactone ring pair. 

These strategies guide the retrosynthetic conversion of 272 to 278 and the further conversion of 278 via 279 to 282. The r-butyl substituent actuates the clearability of the stereocenters in 279. Further retrosynthetic simplification as dictated by basic FG-, stereochemical and topological strategies then leads from 280 to 281 and to 282, a previously described substance. The successful synthesis followed closely the above outlined retrosynthetic scheme. An enantioselective process was devised for the synthesis of 281 from 282 (see Section 10.12).67, 83 

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The multistrategic retrosynthetic analysis of ginkgolide B, which led to the synthesis outlined below, is presented in Section 6.7 of Part One. The synthetic route, an enantioselective version of which was demonstrated, also led to ginkgolide A. 

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