Total synthesis of (.+-.)-granaticin

Asymmetric total synthesis of (−)-lingzhiol via a Rh-catalysed [3+2] cycloaddition

“…Given that the benzylic position could readily undergo a radical-mediated halogenation reaction, we designed a stepwise protocol involving sequential halogenation/ substitution/oxidation reactions to achieve this transformation. Following a period of experimentation, it was established that substrate 36 could be effectively converted to ketone 37 in 73% yield by the sequential treatment of 36 with N-bromosuccinimide (NBS) in the presence of benzoyl peroxide 68 , as well as a trace amount of water in carbon tetrachloride, followed by MnO 2 -mediated oxidation of the resultant benzylic alcohol in CH 2 Cl 2 at room temperature. Finally, removal of the both methoxyl groups of 37 with AlCl 3 in the presence of an excess of t BuSH in CH 2 Cl 2 resulted in the formation of ( À )-lingzhiol in 78% yield.…”

Synthesis of the BCD‐Ring Substructure of Granaticin A

“…[16] The reaction of ketone 6 with (1-ethoxyvinyl)lithium, [12] which was transmetallated to the less basic organocerium reagent, provided the corresponding tertiary alcohol, which gave, after acid cleavage of the enol ether and elimination of water, α,β-unsaturated ketone 7, together with β,γ-unsaturated ketone 8. [16] The reaction of ketone 6 with (1-ethoxyvinyl)lithium, [12] which was transmetallated to the less basic organocerium reagent, provided the corresponding tertiary alcohol, which gave, after acid cleavage of the enol ether and elimination of water, α,β-unsaturated ketone 7, together with β,γ-unsaturated ketone 8.…”

“…[11] The Yoshii group successfully achieved the stereoselective synthesis of the 2-oxa-6562 naphthoquinone B-ring was prepared by addition of an aryllithium intermediate to an anhydride followed by a Friedel-Crafts cyclisation mediated by AlCl 3 and Mg(OTf) 2 . bicyclo [2.2.2]oct-5-ene substructure that culminated in the first and only total synthesis of racemic granaticin A, [12] followed by the synthesis of the enantiomerically pure natural product. bicyclo [2.2.2]oct-5-ene substructure that culminated in the first and only total synthesis of racemic granaticin A, [12] followed by the synthesis of the enantiomerically pure natural product.…”

“…[16] The reaction of ketone 6 with (1-ethoxyvinyl)lithium, [12] which was transmetallated to the less basic organocerium reagent, provided the corresponding tertiary alcohol, which gave, after acid cleavage of the enol ether and elimination of water, α,β-unsaturated ketone 7, together with β,γ-unsaturated ketone 8. The 2-oxabicyclo[2.2.2]oct-5-ene substructure was accessible stereoselectively using a Sharpless asymmetric dihydroxylation and a diastereoselective ketone reduction in combination with Yoshii's route.…”

A model for the synthesis of naturally occurring benzisochromenequinones

“…2 The pyran ring of the targets has the potential for three asymmetric centres, and considerable effort has been expended in achieving the desired stereochemistry, both for the racemates [3][4][5][6] and for the enantiopure compounds. [7][8][9] Naturally occurring benzisochromenequinones have also been reported, 1 although their syntheses have hitherto received less attention.…”