Titanium(II)‐Mediated Cyclizations of (Silyloxy)enynes: A Total Synthesis of (‐)‐7‐Demethylpiericidin A₁.

Abstract

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Total Syntheses of Parthenolide and Its Analogues with Macrocyclic Stereocontrol

“…Under standard TBAF or TFA conditions, no desired alcohol 16 was detected, and the starting material decomposed to a complex mixture. Fortunately, TBDPS deprotection of 15 was achieved using HF-pyridine in 91% yield . The formed primary alcohol 16 was subjected to the standard SAE reaction to produce compound 17 , which underwent oxidation to yield the corresponding aldehyde 18 .…”

“…Fortunately, TBDPS deprotection of 15 was achieved using HF-pyridine in 91% yield. 16 The formed primary alcohol 16 was subjected to the standard SAE reaction 17 to produce compound 17, which underwent oxidation to yield the corresponding aldehyde 18. At this juncture, we poised to investigate the cyclization of 18 to construct the desired 10-membered ring.…”

“…The resulting mixture was stirred for 2 h, concentrated under reduced pressure and purified by column chromatography (0−1% ethyl acetate/hexane) to afford 15 as a colorless oil (447 mg, 0.831 mmol, 83%). 1 H NMR (400 MHz, CDCl 3 ): δ 7.76−7.64 (m, 4H), 7.45−7.33 (m, 6H), 6.99 (t, J = 7.6 Hz, 1H), 5.39 (t, J = 6.0 Hz, 1H), 5.17 (t, J = 6.2 Hz, 1H), 4.32 (s, 2H), 4.23 (d, J = 6.0 Hz, 2H), 3.79 (s, 3H), 2.42 (q, J = 7.6 Hz, 2H), 2.16 (t, J = 7.6 Hz, 2H), 2.15−2.04 (m, 2H), 1.99 (t, J = 7.6 Hz, 2H), 1.63 (s, 3H), 1.45 (s, 3H), 1.05 (s, 9H); 13 (2Z,6E,10E)-Methyl 2-(chloromethyl)-12-hydroxy-6,10-dimethyldodeca-2,6,10-trienoate (16). To a solution of 15 (33 mg, 0.06 mmol) in THF (1 mL) was added pyridine hydrofluoride (70%, 0.14 mL, 1.0 mmol).…”

“…1 H NMR (400 MHz, CDCl 3 ): δ 6.95 (t, J = 7.6 Hz, 1H), 5.36 (t, J = 6.4 Hz, 1H), 5.13 (t, J = 6.5 Hz, 1H), 4.29 (s, 2H), 4.11 (d, J = 6.8 Hz, 2H), 3.76 (s, 3H), 2.39 (q, J = 7.2 Hz, 2H), 2. 16 (2Z,6E)-Methyl 2-(chloromethyl)-9-((2R,3R)-3-(hydroxymethyl)-2-methyloxiran-2-yl)-6-methylnona-2,6-dienoate (17). In a 10 mL round-bottom flask, 4 Å molecular sieves (100 mg) were dispersed in anhydrous CH 2 Cl 2 (2.8 mL).…”

“…1 H NMR (400 MHz, CDCl 3 ): δ 7.74−7.67 (m, 4H), 7.48− 7.34 (m, 6H), 5.97 (d, J = 0.8 Hz, 1H), 5.95 (s, 1H), 5.39 (t, J = 6.0 Hz, 1H), 5.20 (t, J = 6.4 Hz, 1H), 4.28−4.16 (m, 3H), 2.26 (dd, J = 9.6, 4.9 Hz, 1H), 2. 16 (24.8 mL) was added n-Bu 3 P (0.92 mL, 3.677 mmol) at room temperature under Ar. After 2 h, the reaction mixture was concentrated and purified by column chromatography (0−1% ethyl acetate/ hexane) to provide 21a (748 mg, 1.481 mmol, 60%) and 21b (250 mg, 0.495 mmol, 20%).…”