Total Synthesis of 3‐Oxo‐ and 3β‐Hydroxytauranin via Negishi Coupling of a Bis(ortho‐oxy)‐Functionalized Benzyl Chloride

Abstract

The first asymmetric synthesis of the sesquiterpene quinones 3‐oxo‐ and 3β‐hydroxytauranin (1, 2) was achieved and the originally proposed structure of 3α‐hydroxytauranin was revised. The protected benzyl chloride 5 was obtained in six steps starting from 4‐bromo‐3,5‐dihydroxybenzoic acid (8) via a highly scalable approach. The troublesome Negishi coupling of the benzyl chloride 5 with alkenyldimethylalane 6 was optimized to furnish all‐trans‐farnesylarene 14 in very good yield. This prenylated arene was transformed in six additional steps to 3β‐hydroxytauranin (2). Finally, a new convenient access to propargylated terpenes without using dry cryogenic ammonia and gaseous allene or propyne is described.

Biomimetic Total Synthesis of (±)‐Homodimericin A

“…Substantially pure compound 9 (9:9' > 20:1) was obtained via extensive chromatography,a nd was used in subsequent investigations. [10] To synthesize quinone 3,d ifferent oxidants were examined for the oxidation of resorcinol 9,s uch as PbO 2 ,P hI-(OAc) 2 ,P hI(TFA) 2 , [11] MnO 2 ,a nd K 2 NO(SO 3 ) 2 (FrØmys salt). [12] To our surprise,w ef ound that five equiv of FrØmys salt directly oxidized resorcinol 9 to adimeric compound 7' in 14 %y ield in am ixture of THF and pH 8p hosphate buffer (Scheme 2) at room temperature.…”

Catalytic, Enantioselective, Intramolecular Sulfenoamination of Alkenes with Anilines

“…The 2,6-diisopropylphenyl sulfide moiety was cleanly reduced by lithium naphthalenide, along with the concomitant reductive cleavage of the tosyl protecting group ( Scheme 9 ). 25 The absolute configuration of the reduced product, 2-methylindoline, was compared to literature values and assigned the ( R )-configuration. 26 …”

Biomimetic Total Synthesis of (±)‐Homodimericin A

“…To synthesize quinone 3 , different oxidants were examined for the oxidation of resorcinol 9 , such as PbO 2 , PhI(OAc) 2 , PhI(TFA) 2 , MnO 2 , and K 2 NO(SO 3 ) 2 (Frémy's salt) . To our surprise, we found that five equiv of Frémy's salt directly oxidized resorcinol 9 to a dimeric compound 7 ′ in 14 % yield in a mixture of THF and pH 8 phosphate buffer (Scheme ) at room temperature .…”