Synthetic studies toward Illudins and Ptaquilosin. A highly convergent approach via the dipolar cycloaddition of carbonyl ylides

Using ring-opening reactions of oxabicyclic compounds as a strategy in organic synthesis

“…These cycloadditions are generally highly regioselective and the exo isomer tends to predominate (Scheme 2). The reaction conditions are sufficiently mild that sensitive groups such as cyclopropyl substituents and acetals are tolerated [72][73].…”

“…Subsequent Grob fragmentation leading to scission of the ring junction bond generated the decadienone 239 which has been transformed into periplanone B. Carbonyl groups alpha to the bridging oxygen undergo reduction in the presence of samarium iodide, resulting in ketyl radical anion formation and fragmentation of the carbon-oxygen bond. This reductive ring opening was used by Padwa in synthetic studies toward ptaquilosin [72]. Treatment of 240 with SmI2 generated 241 which contains the basic skeleton of the targetmolecule.…”

Intramolecular isomünchnone cycloaddition approach to the antitumor agent camptothecin

“…18 Dehydration of this intermediate could then be accomplished under acetylation conditions to provide in 89% yield the unsaturated sulfone 21. Dehydrogenation of this compound in the presence of DDQ, followed by sulfone reduction with Raney-nickel in refluxing ethanol, gave pyridone 9 in 81% yield (56% from 19).…”

The interaction of rhodium carbenoids with carbonyl compounds as a method for the synthesis of tetrahydrofurans

“…Products of five-ring carbonyl ylide cycloaddition derived from a-diazoketone (26) can undergo cleavage of the oxabicyclic ring system to produce the core structure of the illudin (25) and ptaquiloxin family of sesquiterpenes [31]. This strategy provides for a rapid assembly of the basic core unit of the target molecules having most of the functionality in place (Scheme 7).…”