Organocuprate‐Initiated Domino Michael–Intramolecular Aldol Reaction – Application to the Formation of Ring B of the Aglycon of Landomycins

Abstract

International audienc

Total Synthesis of the Hamigerans

“…Removal of the benzyl group and subsequent PCC oxidation furnished the ketone 24 , which was efficiently converted into 16 . The aryltriflate 25 was derived from 2,6‐dimethoxy‐4‐methylbenzaldehyde in two steps and then transformed into the pinacol boronate 17 by Miyaura's protocol involving palladium‐catalyzed borylation with bis(pinacolato)diboron.…”

“…[17] Extensive screening of reaction conditions using various Lewis and Brønsted acids showed that the reaction could be promoted using ac atalytic amount (10 mol %) of trifluoromethanesulfonic acid, thus providing the aldehyde 21,having aq uaternary carbon atom (C9), as as ingle diastereomer. Adding 1,2-bis(trimethylsiloxy)ethane to the reaction mixture directly protected the aldehyde group as ad ioxolane, thus affording 22 in 79 %yield over two steps.Removal of the benzyl group and subsequent PCC oxidation furnished the ketone 24,w hich was efficiently converted into 16.T he aryltriflate 25 was derived from 2,6-dimethoxy-4-methylbenzaldehyde in two steps [19] and then transformed into the pinacol boronate 17 by Miyauras protocol [18] involving palladium-catalyzed borylation with bis(pinacolato)diboron.…”

Total Synthesis of (−)-Amovillosumin A and Structure Correction of (−)-Amovillosumin C Using Chemical Synthesis

“…The spectroscopic data were in accordance with the reported values. 18 IR ν max (film)/cm −1 2844, 1662, 1571, 1467, 1238, 813; 1 H NMR (CDCl 3 , 400 MHz) δ 10.44 (1H, s, CHO), 6.37 (2H, s, H-3), 3.87 (6H, s, OMe) and 2.36 (3H, s, CH 3 ); 13 6-Hydroxy-2-methoxy-4-methylbenzaldehyde (11). Anhydrous AlCl 3 (7.80 g, 58.50 mmol) was added portionwise over 5 min to a stirred solution of aldehyde 10 (8.78 g, 48.73 mmol) in dry CH 2 Cl 2 (95 mL) under nitrogen.…”

Conceptual advances in nucleophilic organophosphine-promoted transformations

“…Several efforts to achieve the desired transformation of β,β-disubstituted α,β-unsaturated electron withdrawing systems have been realised to be unsuccessful or not widely applicable. 16 The primary reason could be the incompatible nucleophilicity of the Lewis bases and the steric encumbrance of the β,β-disubstituted activated olefins.…”