An Oppolzer's sultam-based highly stereoselective α-hydroxylation of amides was developed to deliver the desired products in good yield and excellent diastereoselectivity (>20/1). The generally crystalline products and the recyclability of the chiral auxiliary illustrate the practicability and scalability of the current approach.
An efficient bioinspired approach to the total synthesis of (±)-cafestol features a late-stage installation of the furan ring with a mild Au-catalyzed cycloisomerization. The Et2AlCl-promoted aldehyde-ene cyclization and subsequent Friedel-Crafts reaction deliver a requisite tricyclic system in gram scale with high stereo- and regioselectivity. Moreover, a highly stereoselective SmI2-mediated aldehyde-alkene radical cyclization furnishes the key bicyclo[3.2.1]octane skeleton to offer an advanced intermediate for the synthesis of other oxygenated ent-kaurene diterpenoids.
An organocatalytic cross-aldol reaction of formaldehyde (formalin) with alkyl aldehydes, followed by the Z-selective Horner-Wadsworth-Emmons (HWE) reaction and immediate lactonization, afforded γ-alkylated pentenolides in good overall yields and excellent enantioselectivities. Based on this scalable sequence, five quinolizidine alkaloids were synthesized in a unified and concise manner. The development of an in situ activation of a tertiary amide to improve the efficiency of the Bischler-Napieraiski (B-N) reaction was also noteworthy due to the generality to sensitive substrates for a variety of target molecules.
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