Rearrangements of Cyclobutenones. Synthesis of N-Methyl-7,8-dihydrobenzophenanthridine-9,12-diols and Related Compounds

Tandem Electrocyclic Ring Opening/Radical Cyclization: Application to the Total Synthesis of Cribrostatin 6

A concise total synthesis ofcribrostatin 6 (1), an antimicrobial and antineoplastic agent,was accomplished using a tandem electrocyclic ring opening/radical cyclization sequence. Specifically, intermediate4 underwent a 4π-electrocyclic ring opening, radical cyclization, and homolytic aromatic substitution sequence followed by an oxidation to afford the natural product1in one pot. Owing to the rapid buildup of complexity in the key step, 1 could be synthesized from commercially available starting materials in only four linear steps. Application of this chemistry to the concise syntheses of analogs of cribrostatin 6 (1) is also reported.

Convenient Access to Hydroquinone and Quinone Derivatives from Cyclobutenedione Units

An important synthetic method providing access to a variety of heterocyclic and polycyclic quinones and hydroquinones is described. The key transformation involves the thermal ring expansion of cyclobutenedione derivatives to quinone/hydroquinone units. The synthetic utility and recent applications of this method in natural product synthesis are also discussed.

Total synthesis of cribrostatin 6

Fast and furious: Cribrostatin 6, an antimicrobial and antineoplastic agent, was the target of a total synthesis where the longest linear sequence was only four steps. The key step involves a tandem 4pi electrocyclic ring opening, radical cyclization, and homolytic aromatic substitution sequence to afford the tricyclic core of the natural product.