Syntheses of naphtho[2,3-c]pyran-5,10-quinones using ceric ammonium nitrate

The Synthesis of Ventiloquinone F and Isoventiloquinone F as Racemates

“…Assignment of structure 23 to the first naphthopyran-6,9-quinone to elute is based inter alia on the following one-proton signals for the pyran ring in the 1 H NMR spectrum; a ddd at δ ϭ 2.42 ppm with J ϭ 17.6 Hz for geminal coupling between the diastereotopic 4Ј-H's, J ϭ 11.0 Hz for coupling between 4-H ax and 3-H ax , and J ϭ 1.8 Hz representing coupling between 4-H ax and 1-H ax and is assigned to pseudoaxial 4-H; a ddd at δ ϭ 2.90 ppm with a similar J ϭ 17.6 Hz representing coupling between 4-H eq and 4-H ax , J ϭ 3.0 Hz for coupling between 4-H eq and 3-H ax , J ϭ 1.0 Hz representing coupling between 4-H eq and 1-H ax and is assigned to pseudoequa-Scheme 2. Reagents and conditions: (i) MeMgBr/diethyl ether; (ii) Hg(OAc) 2 /THF/H 2 O/NaOH/NaBH 4 ; (iii) cerium() ammonium nitrate/H 2 O/CH 3 CN torial 4-H; a multiplet at δ ϭ 3.68 ppm assigned to 3-H ax ; a ddq at δ ϭ 4.85 ppm with J ϭ 6.6 Hz representing coupling of 1-H ax to the C1ϪCH 3 , J ϭ 1.8 Hz representing coupling between 1-H ax and 4-H ax , J ϭ 1.0 Hz representing coupling between 1-H ax and 4-H eq and is assigned to the pseudoaxial 1-H. [8,24] The second naphthopyran-6,9-quinone to elute was assigned the structure 25 based on obvious similarities in the 1 H NMR spectrum to quinone 23 with a major difference being in the position of the signal due to 3-H ax which appeared as a multiplet at δ ϭ 3.95 ppm that allowed assignment of a trans-1,3-dimethyl structure. [8,24] Fraction B afforded the two individual naphthopyran-6,7-quinones 24 (18%) and 26 (24%).…”

“…Reagents and conditions: (i) MeMgBr/diethyl ether; (ii) Hg(OAc) 2 /THF/H 2 O/NaOH/NaBH 4 ; (iii) cerium() ammonium nitrate/H 2 O/CH 3 CN torial 4-H; a multiplet at δ ϭ 3.68 ppm assigned to 3-H ax ; a ddq at δ ϭ 4.85 ppm with J ϭ 6.6 Hz representing coupling of 1-H ax to the C1ϪCH 3 , J ϭ 1.8 Hz representing coupling between 1-H ax and 4-H ax , J ϭ 1.0 Hz representing coupling between 1-H ax and 4-H eq and is assigned to the pseudoaxial 1-H. [8,24] The second naphthopyran-6,9-quinone to elute was assigned the structure 25 based on obvious similarities in the 1 H NMR spectrum to quinone 23 with a major difference being in the position of the signal due to 3-H ax which appeared as a multiplet at δ ϭ 3.95 ppm that allowed assignment of a trans-1,3-dimethyl structure. [8,24] Fraction B afforded the two individual naphthopyran-6,7-quinones 24 (18%) and 26 (24%). Assignment of the cis structure 24 to the first 6,7-quinone to elute was based on the comparative one-proton signals of its 1 H NMR spectrum to quinone 23.…”