I2–PPh3 mediated spiroannulation of unsaturated β-dicarbonyl compounds. The first synthesis of (±)-negundoin A

Abstract

An efficient and stereoselective spiroannulation of unsaturated enols is reported. Unsaturated β-dicarbonyl compounds undergo cyclization by reaction with catalytic I2-PPh3, affording the corresponding spiro enol ether derivatives, with complete regio- and stereoselectivity, under mild conditions. Utilizing this new methodology, the first total synthesis of the anti-inflammatory diterpene negundoin A and a naturally occurring trypanocidal aldehyde is reported.

Base Promoted Intramolecular O‐arylation For The Synthesis of Dibenzo[b,f]oxepinones Toward Dihydroartocarpol D

“…The structure of compound 8 was unambiguously confirmed by X-ray single crystal diffraction. [16] Second, I 2 -PPh 3 mediated cyclization [17] of 5 q resulted in the formation of dihydrodibenzo[b,f]pyrano[2, 3-d]oxepine 9 in 78% isolated yield (Scheme 4). Inspired by the result, the strategy was further extended to the synthesis of dihydroartocarpol D. As shown in scheme 5, TfOH-promoted acylation of resorcinol with commer- [c] K 2 CO 3 (2.5) toluene 120 24 0 0 12 [c] K 2 CO 3 (2.5) dioxane 120 24 0 0 13 K 2 CO 3 (2.5) DMF 130 24 74 0 14 [e] K 2 CO 3 (2. cially available (4-bromo-2-fluorophenyl)acetic acid 10 provided ketone 12 in 90% isolated yield.…”

The first synthesis of (−)-isoambreinolide, (+)-vitexifolin D and (+)-vitedoin B

“…1 H NMR (CDCl 3 , 500 MHz) δ: 0.72 (s, 3H), 0.85 (s, 3H), 0.87 (s, 3H), 1.26-1.45 (m, 3H), 1.56-1.92 (m, 7H), 1.97 (ddd, J = 12.9, 12.9, 5.0 Hz, 1H), 2.05 (s, 3H), 2.20 (m, 1H), 2.40 (ddd, J = 13.0, 4.1, 2.5 Hz, 1H), 2.52 (m, 1H), 4.52 (dd, J = 11.9, 4.4 Hz, 1H), 4.51 (s, 1H), 4.87 (s, 1H). 13 C NMR (CDCl 3 , 125 MHz) δ: 14.4 (CH 3 ), 16 3-((1S,4aR,5R,8aR)-5-Methoxycarbonyl-5,8a-dimethyl-2-methylene-decahydronaphthalen-1-yl)propanoic acid (8). Colourless oil.…”

“…Colourless syrup; 1 H NMR (CDCl 3 , 500 MHz) δ ( ppm): 0.86 (d, J = 6.7 Hz, 3H), 0.88 (s, 3H), 0.95 (s, 3H), 1.24 (m, 1H), 1.41-1.45 (m, 2H), 1.49-1.53 (m, 2H), 1.67 (m, 1H), 1.86 (ddd, J = 13.6, 11.2, 5.1 Hz, 1H), 2.18 (ddd, J = 13.5, 11.5, 8.4 Hz, 1H), 2.49 (ddd, J = 18.7, 11.3, 5.1 Hz, 1H), 2.56 (ddd, J = 18.7, 11.2, 8.4 Hz, 1H). 13 15.1 (CH 3 ), 16.9 (CH 3 ), 18.0 (CH 2 ), 21.9 (CH 3 ), 22 (1S,2R,4aR,5R,8aR)-2′,5′,8′a-Trimethyl-5′-methoxycarbonyl-spiro-[furan-2(5H),1′(2′H)-decahydro naphthalen]-5-one (16). Colourless oil.…”

“…15 The I 2 -PPh 3 mediated spirocyclization of unsaturated β-dicarbonyl compounds, with complete regio-and stereoselectivity, was also communicated very recently by the present authors. 16…”

Acid-catalyzed chemoselective C- and O- prenylation of cyclic 1,3-diketones

“…The synthesis of 5-chromenone derivatives is generally achieved using the cost-effective and commercially available 1,3-cyclohexanedione as the starting material (Scheme 2). Only a two-step procedure is required to prepare 5-chromenone derivatives from 1,3-cyclohexanedione and either prenyl bromide [7][8][9] or bromo-substituted benzyl bromide [10]. Owing to its atom-and step-economy, the [3+3] annulation of 1,3-cyclohexanedione with unsaturated precursors represents a more convenient and straightforward strategy.…”