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Catalytic Asymmetric Formal Total Synthesis of ( − )-Triptophenolide and (+)-Triptolide

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ABSTRACT

Abstract: Catalytic asymmetric formal synthesis of (−)-Triptophenolide and (+)-Triptolide have been achieved. Key reaction involves Palladium catalyzed asymmetric conjugate addition of aryl boronic acid to 3-methyl cyclohexe-1-none to form quaternary carbon. Claisen rearrangement and subsequent aldol reaction furnished trans-decaline key intermediate, which assured a formal total synthesis of (−)-Triptophenolide and (+)-Triptolide.

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Successful claisen rearrangement
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Sch3: Successful claisen rearrangement

Mentions: As illustrated in Scheme 2, tautomerization of ketone into enol was the reason of side reaction. Consequently, prevention of the tautomerization by reduction of ketone with NaBH4 could be a choice. In fact, under the same thermo condition, ortho-claisen rearrangement of 14 afforded diol 15 in 71 % yield (Scheme 3). Routine methyl protection of phenol and subsequent PCC oxidation produced ketone 5 in 87 % yield in 2 steps.Scheme 3


Catalytic Asymmetric Formal Total Synthesis of ( − )-Triptophenolide and (+)-Triptolide
Successful claisen rearrangement
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Related In: Results  -  Collection

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Sch3: Successful claisen rearrangement
Mentions: As illustrated in Scheme 2, tautomerization of ketone into enol was the reason of side reaction. Consequently, prevention of the tautomerization by reduction of ketone with NaBH4 could be a choice. In fact, under the same thermo condition, ortho-claisen rearrangement of 14 afforded diol 15 in 71 % yield (Scheme 3). Routine methyl protection of phenol and subsequent PCC oxidation produced ketone 5 in 87 % yield in 2 steps.Scheme 3

View Article: PubMed Central - PubMed

ABSTRACT

Abstract: Catalytic asymmetric formal synthesis of (−)-Triptophenolide and (+)-Triptolide have been achieved. Key reaction involves Palladium catalyzed asymmetric conjugate addition of aryl boronic acid to 3-methyl cyclohexe-1-none to form quaternary carbon. Claisen rearrangement and subsequent aldol reaction furnished trans-decaline key intermediate, which assured a formal total synthesis of (−)-Triptophenolide and (+)-Triptolide.

Graphical abstract"/>