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Quinone Lit Talk Quinones in Organic Chemistry: Synthesis of and Applications Towards Natural Products H3C CH3 H H H3C OH H OH O N CH3 O CH3 O HO O Tetrapetalone A (revised structure) TL, 2003, 44, 7417 Literature Presentation Ryan Zeidan Stoltz Group Meeting 2/16/04 Outline of Quinones I. Introduction to Quinones A. Nomenclature B. Biochemistry C. Biosynthesis II. Synthesis of Quinones via Oxidation A. Fremy's Salt B. CAN C. LTA D. DDQ E. Air III. Other Syntheses of Quinones/Uses A. Boronic Esters B. Indoles C. DMP oxidation of anilides D. Cyclobutenediones E. Benzoin reaction IV. Applications to Natural Products A. Aflatoxin B B. Elisabethin A C. Lemonomycin 1 Quinone Background - Nomenclature OH OH O O O OH O Phenol Hydroquinone p-Quinone o-Quinone O O O R N R OH Quinol o-Quinone methide p-Quinone methide o-Quinone methide imine Redox Process -2e- Hydroquinone Quinone + 2 H+ 2e- O H O O - H - H H H O H O H O hydroquinone semiquinone quinone OH O OH O Jones AgO2 SnCl or SnCl2 2 O NaBH4 OH OH O 2 Quinones in Nature - Ubiquinones mediate electron transfer processes involved in energy production through their redox reactions: O OH MeO Me MeO Me + NAD+ NADH + H+ + Reduced MeO R MeO R Oxidized form form O OH OH O MeO Me MeO Me + 1/2 O 2 + H2O MeO R MeO R OH O + NAD+ + H O Net Change: NADH + 1/2 O2 + H 2 Biosynthesis of Quinones: Pentaketides O O O OH OH SCoA O O O O O O CoAS O HO OH O O OH O HO OH O O O O MeO OMe O O O SCoA O OH O 3 Biosynthesis Continued Heptaketides: O OH O O O HO OMe HO OMe O O O O O O SCoA O O O OH O O Octaketides: OH O Me OH OH Me O O NADH NAD+ O O O SCoA O O O O O O O O O H O O OH OH Me OH O Me O O O HO O HO O O A Representative Difficulty in Direct Oxidation of Arenes O Br Br Br Br O HNO3 H2SO4 Fremy's salt NO2 OH Br Br 1. H2NNH2, Pd/C 2. NaNO2, H2SO4 + Br H3O Br - Direct oxidation of the unactivated arene was not achievable - A round about sequence of nitration, reduction, diazotization, displacement by hydroxide and finally oxidation of the phenol was necessary to form the quinone - Unactivated arenes present a difficulty in quinone synthesis 4 Fremy's Salt A Typical Example: OH COMe O COMe O COMe N N MeO N (KSO3)2NO SPh (Fremy's salt) O O MeO O CO2Me CO2Me CO2Me O SPh O O COMe O COMe N N KHCO3 (KSO3)2NO MeO O (Fremy's salt) MeO O CO2Me CO2Me O O JOC, 1981, 46, 2426. - Fremy's salt oxidizes most phenols to p-quinones when there is no para substituent Fremy's salt = on the phenol - Salt is a stable free radical that oxidizes via a free radical mechanism - Oxygen incorporation occurs exclusively from the oxygen of Fremy's salt O N KO3S SO3K Fremy's Salt (cont'd) Gives o-quinones when para position is substituted: OH O Fremy's salt O 90% MeO2C MeO2C NH CO2Me NH CO2Me Fremy's salt 93% HO N CO2Me O N CO2Me O MacKenzie, A. R. Tetrahedron, 1986, 42, 3259 O A more oganic soluble form of Fremy's catalyst = N Ph O 5 Fremy's Salt Mechanism H O O O O + N KO3S SO3K H O N KO3S SO3K O O O H O O N(SO K) N(SO3K)2 O R 3 2 -O18 isotope experiments showed that oxygen incorporation was exclusively from Fremy's salt oxygen CAN Oxidations OMe O O O CAN O MnO2 O MeO O O HO C 32% 2 89% HO2C O O pleurotin JACS, 1988, 11, 1634 OH O OH CAN Na2S2O4 MeO OMe O OMe HO OMe Me Me Me JACS, 2003, 125, 4680 - CAN is the reagent of choice for oxidative demethylation of methoxyarenes - CAN/Na2S2O4 sequence provides an overall net demethylation of methoxyarenes - CAN is (NH4)2Ce(NO3)6 6 LTA Oxidations OH O O OH H OH LTA OH 73% H OH O OMe O OH OMe J. Chem. Soc., P.T. 1, 1985, 525 - LTA can cause an oxidative isomerization O O O OH O H N AcN + HO 2 LTA, DCM 1. H 0oC 2. H2, Pd/C N 40% N 93% N Bn O Bn O H O JOC, 1988, 53, 5355 - Oxidation of the aniline to the o-quinoneimide occurs in modest yield DDQ Oxidations OH OH OH O DDQ 95% OH O MeO OMe MeO OMe OMe OMe JOC, 1999, 64, 1720 HO O O Cl Cl Cl Cl Cl Cl OH O O DDQ R R R N N N H H H Org. Lett., 2001, 3, 365 - DDQ is a competant oxidant for quinone formation, although CAN is more robust and typically higher yielding 7 MeO Air Oxidation MeO HO O OH OH HO HO O OH O OH O OH O OH O air, THF, H2O O 24 hours, RT HN 74% HN R R Kita, Y. JACS, 2001, 123, 3214 Saframycin G: OMe OMe HO HO O H O H H H OH OH N N NaHCO3 N OH N OH MeO air MeO H 69% H O O NH NH O O O O Chem. Pharm. Bull., 1995, 43, 777. Quinone Boronic Esters OH R' R R R O 2 Cr(CO) + R B 5 2 O MeO O R' B OMe O O O R R CAN 2 R R PdCl2(dppf), R3Br 2 O R' B R' R3 O O O - Allows for regioselective hydroquione formation - Cerium oxidation of crude reaction mixture afforded quinones in good yields - Quinone boronic esters were reactive in Suzuki couplings to give unsymmetrical quinone products as single regioisomers Harrity, J. P. A., et. al. J. Org. Chem., 2001, 66, 3525 8 Synthesis of Indoles from Quinones O R2 NBz R1 NHBz R1 NHBz R R2 Diels-Alder 2 1. OsO4 R1 + + H 2. NaIO4 R4 R3 R3 MeO OMe R4 OMe R4 OMe R3 O Bz R2 N R Indoles made in 32-70% overall yields with wide range of TsOH 1 substitution tolerated R4 Kerr, M. A., et. al. Org. Lett, 2001, 3, 3325. OMe R3 O DMP Oxidations O H H N N DMP, H2O O 43% O O Mechanism: AcO O O O OAc I O I OAc OAc - AcO O Me O AcO I O I I O - O AcO O R O O O -AcOH B H H -AcOH N R O N O N O R O O I DMP + H2O O AcO Nicolau, K.C. JACS, 2002, 124, 2212. 9 DMP Oxidation (cont'd) O R B OAc O R I - O N H HN O O O O O I I O O AcO O AcO O O R HN O O O H N H DMP, H2O N O 40% H O H Nicolau, K.C. JACS, 2002, 124, 2212. Regiospecific Synthesis of Quinones from Cyclobutenediones O O R1 O R R 1 3 R1 R3 Heat Heat R3 R2 R OH 2 R2 R1 O OH O R2 O OH O R1 O R1 Heat R1 CAN R2 R2 OH R2 OH O - For synthesis of cyclobutenediones see JOC, 1988, 53, 2477. Liebeskind, L. S., et. al. J. Org. Chem., 1992, 57, 4345 10 Benzoin Reaction Approach to Quinones O N OMOM O N OMOM 5 mol% cat 10 mol% DBU tBuOH, 40oC O OH 0.5 hr, 95% O O Et Me cat = N Br- HO S O N OMOM OH NH OMOM OH O OMOM 1. Pd/C, H , rt 2 aq. H2SO4 2. air, 110oC MeOH, dioxane rt, 86% OH 75% O O O - Crossed aldehyde-ketone benzoin reaction worked well for a variety of substrates - Substitution allows access to functionalized anthraquinones Suzuki, K. JACS,, 2003, 125, 8432 Quinone Approach to Aflatoxin B2 O p-tol O p-tol Br S S MOMO 1, BuLi MOMO CAN O 2. auxiliary MeO OMOM MeO OMOM MeO O O p-tol O p-tol O S S H H HO HO Raney Ni, EtOH O + O TiCl4(5 eq) 100% Ti(OiPr)4 (5 eq) O H 65% MeO MeO O H 1 3.3 O O H O HO H O O MeO O H MeO O H aflatoxin B2 Noland, W. E. Org. Lett., 2000, 2, 2109 11 Mechanism of Furan Addition O p-tol O p-tol S S H O Conjugate HO Re-aromatize Addition O MeO O O MeO O O p-tol O p-tol S S O HO Cyclization HO O MeO O MeO O Chem. Lett., 1987, 2169 Total Synthesis of Elisabethin A: IMDA Using a Quinone Me Me OTBS TBAF OH FeCl3 (aq) 91% TBSO OMe HO OMe Me Me Me Me Me H 1. Pd/H H Me H 2 Me H O O 2. NaOH O 3. BBr3 O OMe O OMe O OH Me Me Me elisabethin A Mulzer, J. JACS, 2003, 125, 4680. 12 IMDA Transition State Me H Me H H O O Me OMe Minimizing allylic strain controls facial selectivity in the DA transition state, taken into account with an endo approach gives rise to the observed selectivity Stoltz Lab Quinone Work: Lemonomycin HO HO OH OH OMe O H H H H N CAN(aq) N N N MeO 0oC MeO OH OH 51% O OH O O OH OH O O N N Ashley, E.R.; Cruz, E.
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