Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

The stereocontrolled synthesis of the C(17)–C(28) fragment 3 of didemnaketal B was accomplished in 21 steps from the natural (R)-(+)-pulegone and (S)-(−)-citronellal. The key steps involved diastereoselective construction of two chiral carbon centers through the intramolecular chiral induction and uncommon Julia olefination of ketone forming the E-trisubstituted C(22)–C(23) double bound.

A synthetically useful Wagner–Meerwein (WM) rearrangement is reported in this paper. The investigation on the design and optimization involved the substrates α-quaternary β-bromovinyl methyl ethers as well as the reaction conditions. γ-Aryl α,β-unsaturated aldehydes with versatile synthetic uses could readily be obtained through a special pathway in high yields. For example, tricyclic aromatic systems were constructed efficiently through a tandem WM rearrangement/Friedel–Crafts alkylation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The fully substituted cyclopentenedione core of madindoline A (1) and B (2) as potent and selective inhibitor of IL-6 has been synthesized efficiently. The quaternary carbon center C-2′ was constructed on the basis of a newly developed AlEt₃-promoted tandem reductive rearrangement of α-hydroxy epoxides.

The easily prepared and recoverable chiral N-sulfonylated β-amino alcohol 2 in combination with Ti(OPr-i)₄was found to be an effective chiral catalyst for the enantioselective addition of alkynylzinc to ketones, which gave the useful products, i.e. chiral tertiary propargyl alcohols, with the ee up to 92%.

A novel and general approach for synthesis of the multi-oxygenated dihydrofuran sesquiterpenes has been developed starting from santonin. The key steps involve: the strategic acid-catalyzed double-bond shifting affording 4, the novel base-promoted epoxide rearrangement of 5 generating two key functionals (the C5-OH and the Δ^7,11 double bond), and the stereoselective cyclization of tetrahydrofuran ring without pre-controlling the stereochemistry of C-7. As an example of this approach, synthesis of (+)-2,14-deoxyalatol was described in detail.

A facile and highly diastereoselective method for the construction of 2-quaternary 1,3-amino alcohols and 1,3-diols has been developed on the basis of the AlEt₃/THF-promoted tandem rearrangement/reductive reaction of α-hydroxy (amino) aziridines (epoxides). The progressive achievement in this article included that both 2-epimers of the units could be constructed from the initially same substrate. Also a stereochemistry assignment we reported previously was corrected.

Drei benachbarte Stereozentren, zwei davon mit einem quaternär substituierten Kohlenstoffatom, werden durch eine Tandem-Semipinacol-Umlagerung/Alkylierung von α-Epoxyalkoholen mit RB(OH)₂ effizient und stereoselektiv aufgebaut (siehe Schema).

Three contiguous stereocenters, two of which are quaternary carbon atoms, were efficiently and stereoselectively constructed by a tandem semipinacol rearrangement/alkylation of α-epoxy alcohols with RB(OH)₂ (see scheme).

A novel and highly diastereoselective samarium-catalyzed tandem rearrangement/reduction of secondary α-hydroxy epoxides, which involves a C1 to C3 carbon migration rearrangement and a very interesting hetero-Tishchenko reduction of the intermediate aldehyde and the reductant aldehyde, has been reported. This reaction could be developed to provide a facile and stereoselective construction of 2-quarternary 1,3-diol units with an hydroxymethyl moiety attached to the diastereogenic quaternary carbon center. Detailed investigations have been carried out concerning the screening of the aldehydes as a reductant, the optimization of reaction conditions, and the substrate scope of this tandem reaction. A catalytic cycle for this reaction, the electronic and steric effects of the reductant aldehydes, and the mechanism for the acyl migration of 1,3-diol monoesters are proposed.

Drei benachbarte Stereozentren werden in einer neuen Samarium-katalysierten Konsekutivreaktion hoch diastereoselektiv erzeugt. Ausgehend von α-Hydroxyepoxiden 1 entstehen ausschließlich die C1,C2-anti-Isomere der Produkte 2 und 2′. Aus der Reaktion ließe sich ein allgemeines Verfahren für die Synthese von 1,3-Diolen mit quartärem Stereozentrum in der 2-Position entwickeln.

Three contiguous stereocenters are constructed with high diastereoselectivity in a novel samarium-catalyzed tandem reaction of α-hydroxy epoxides 1 to give exclusively the C1,C2-anti isomers of 2 and 2′. This could lead to the development of a general procedure for the diastereoselective construction of 2-quaternary 1,3-diol units.