Rhododaurichromanic acids

The two novel chromane derivatives rhododaurichromanic acids A and B [19] as well as the known Daurichromenic acid [20] are members of a new interesting class of anti-HIV agents and are therefore attractive synthetic targets (Scheme 3). These compounds were successfully synthesized by Z. Jin et al. [21] in good overall yields, applying a microwave-assisted tandem condensation and intramolecular S -type cyclization to form the... 

Scheme 3 Microwave-assisted synthesis of Daurichromenic Acid and Rhododaurichromanic Acids A and B...

Developments in the chemistry of the smenochromenes, marine macrolides with a chromene core, include a four-step synthesis of racemic smenochromene D 16 from hydroxyfamesyl acetate and 4-hydroxy-3-methoxyphenyl formate and its conversion into racemic smenochromene B by way of a macroring contraction and bond isomerisation <07T6529>. Several [/>,c]-fuscd chromans, e.g. 17, related to rhododaurichromanic acid and... 

To complete the total synthesis, cycloadducts 119a and 119b were saponified using 6M aq NaOH in THF/MeOH without any complication to give rhododaurichromanic acids A and B (105a and 105b) in 94% overall combined yield before separation viaHPLC (Scheme 12.27) [70]. Despite the... 

After total synthesis of rhododaurichromanic acid by photochemical [2+2] cycloaddition, inspired by the precedents in polyene cyclizations, especially the work of Omura and coworkers [74], we attempted to treat daurichromenic ester 118a with various Lewis acids and mercury reagents but failed, as shown in Scheme 12.28. Fortunately, the outcome changed when using Brpnsted acids such as TFA, especially when it was used at 30 equiv or as a cosolvent with CH2CI2, we isolated two products 121 and 122 with each as a single diastereomer, the formation of 122 likely proceeds through the classic polyene cyclization via 123 [75]. 

On the other hand, the total synthesis of rhododaurichromanic acid A 105a was achieved via sequential saponification and Burgess elimination from compound 121 (Scheme 12.29). 

The most elegant syntheses of rhododaurichromanic acid A 105a, B 105b, and of daurichromenic acid 113a were reported by Jin and coworkers [77]. Jin s synthesis features a unique microwave-assisted formal oxa-[3+3] cycloaddition of resorcinol derivatives with enals, and provides a rapid and novel approach to chromenes (Scheme 12.32). It also bypasses the DDQ aromatization that was problematic in ours [73] and in the synthesis of Wilson s [76]. Their... 

SCHEME 12.29 Synthesis of rhododaurichromanic acids A 105a and hongoquercin A 126. 

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