Synthesis of espicufolin based on 6-endo ring closure of o-alkynoylnaphthols †

Cyclization of 1-hydroxy-2-(oxoalkynyl)anthraquinones

“…It should be noted that general procedures for the construction of the benzopyrone structure are known 3 and can be used for the synthesis of anthra [1,2 b]pyrantriones. 4,5 It is much more difficult to introduce an unsaturated or another chemi cally labile substituent, which is analogous to those present in kidamycin antibiotics, at position 2 of these compounds.…”

Isolation, Enantioselective Total Synthesis and Structure Determination of the Anthrapyran Metabolite SS 43405‐e

“…The next task was to remove the protecting groups at the anthraquinone moiety and perform the ring closure via an intramolecular 6-endo-dig cyclization to yield the desired final product under acidic conditions in a domino process. [4] Thus, the treatment of a solution of 2 in acetic acid at 60°C with a catalytic amount of sulfuric acid led to cleavage of both the isopropyl ethers followed by intramolecular 6- endo-dig cyclization [10] to yield (S)-SS 43405-e (S)-1 in 81 % yield.…”

Enantioselective Total Synthesis and Structure Determination of the Antiherpetic Anthrapyran Antibiotic AH‐1763 IIa

“…The pyron ring was finally achieved under basic conditions. Thus, treatment of 3 in acetone with Cs 2 CO 3 yielded the tetracycle 22 in 71 % yield 5c,d. 22 In the final steps in the synthesis of (14 S ,16 R )‐AH‐1763 IIa ( 1 ) the isopropyl and benzyl protecting groups were removed by treating 22 with TiCl 4 in CH 2 Cl 2 at −78 °C and then allowing the reaction mixture to warm slowly to 0 °C (yield of 1 : 90 %) 10d…”

“…Despite the excellent work from the research groups led by Hauser,5a,b Uno,5c,d Krohn,5e and McDonald,5f there is still no general approach to the anthrapyran antibiotics, especially those with stereogenic centers in the side chain.…”