Belmar J, Funk RL * Pennsylvania State University, USA
Total Synthesis of (±)-Communesin F via a Cycloaddition with Indol-2-one.
J. Am. Chem. Soc. 2012;
134: 16941-16943
Key words
communesin F - indol-2-one - Diels–Alder cycloaddition - mercuric triflate - trimethyl
aluminum
Significance
The stereochemically complex polycyclic structure of the communesins has attracted
the interest of several researchers and led to the total syntheses of communesin A,
B and F. Funk and co-worker now report an elegant and concise synthesis of the moderately
cytotoxic communesin F that relies on an unusual Diels–Alder cycloaddition of indol-2-one,
a reaction developed by the group. Its considerable synthetic utility has previously
been demonstrated in the total synthesis of perophoramidine and is now further showcased
by the synthesis of communesin F in only 15 steps and an overall yield of 6.7%.
Comment
Indol-2-one B was generated from bromooxindole A and underwent smooth cycloaddition with indole C to afford E via intermediate D. Tosylation of the amide followed by methanolysis led to formation of aminal F. Advanced tetracyclic intermediate G was obtained in three more steps. Heck reaction of G with alcohol H, followed by a high-yielding mercuric-triflate promoted cyclization to the benzazepine
gave I. Cyclization to the bridged lactam J could not be achieved under thermal conditions, but exposure to trimethyl aluminum
effected the desired transformation. Synthetic communesin F was obtained after four
more steps.
