A variety of chroman spiroketals are synthesized via inverse-demand [4 + 2] cycloaddition of enol ethers and ortho-quinone methides (o-QMs). Low temperature o-QM generation in situ allows for the kinetic, diastereoselective construction of these motifs, providing entry to a number of unusual chroman spiroketal natural products.
Download full-text PDF |
Source |
|---|---|
| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2430732 | PMC |
| http://dx.doi.org/10.1021/ol8003244 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Heteryunine A, an amidated tryptophan-catechin-spiroketal hybrid with antifibrotic activity from Heterosmilax yunnanensis.
Bioorg Chem
October 2024
State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, China. Electronic address:
An unprecedented spiro-C-glycoside adduct, heteryunine A (1), along with two uncommon alkaloids featuring a 2,3-diketopiperazine skeleton, heterpyrazines A (2) and B (3), were discovered in the roots of Heterosmilax yunnanensis. The detailed spectroscopic analysis helped to clarify the planar structures of these compounds. Compound 1, containing 7 chiral centers, features a catechin fused with a spiroketal and connects with a tryptophan derivative by a CC bond.
View Article and Find Full Text PDFMechanistic Insights on Pd-Catalyzed Three-Component Reactions of Alkynols, Methyl Orthoformate, and Salicylaldehyde Derivatives. Application to the Synthesis of Steroid Chroman Ketals and Spiroketals with Antioxidant Activity.
J Org Chem
November 2023
Facultad de Química, Universidad Nacional Autónoma de México, CDMX, 04510 Mexico City, Mexico.
Contrary to our previous report in which a Pd-catalyzed three-component reaction of a steroid alkynol, trimethyl orthoformate, and salicylaldehyde exclusively produced chroman ketals, the same reaction employing 2,5-dihydroxysalicylaldehyde led to a mixture of a chroman ketal and a spiroketal. Provided that both courses of the reaction imply a 4 + 2 inverse demand cycloaddition between an -quinone methide and an enol ether, density functional theory calculations revealed that the chroman ketal/spiroketal selectivity is governed by both, the rate of the formation of the -quinone methide and the isomerization of the initially produced exocyclic enol ether─that led to the spiroketal─to its endocyclic partner that produces the chroman ketal. Remarkably, Lewis catalysis is central to the observed reactivity, and the availability of plausible catalytic species controls the overall chemoselectivity.
View Article and Find Full Text PDFCatalytic Control of Spiroketal Formation in Rubromycin Polyketide Biosynthesis.
Angew Chem Int Ed Engl
December 2021
Faculty of Biology, University of Freiburg, Schänzlestrasse 1, 79104, Freiburg, Germany.
The medically important bacterial aromatic polyketide natural products typically feature a planar, polycyclic core structure. An exception is found for the rubromycins, whose backbones are disrupted by a bisbenzannulated [5,6]-spiroketal pharmacophore that was recently shown to be assembled by flavin-dependent enzymes. In particular, a flavoprotein monooxygenase proved critical for the drastic oxidative rearrangement of a pentangular precursor and the installment of an intermediate [6,6]-spiroketal moiety.
View Article and Find Full Text PDFAg/Brønsted Acid Co-Catalyzed Spiroketalization of β-Alkynyl Ketones toward Spiro[chromane-2,1'-isochromene] Derivatives.
Org Lett
July 2017
School of Chemistry and Materials Science, Jiangsu Normal University, Xuzhou 221116, P. R. China.
A new Ag/Brønsted acid co-catalyzed spiroketalization of β-alkynyl ketones with para-quinone methides (p-QMs) has been established, enabling multiple C-C and C-O bond-forming events to access densely functionalized spiro[chromane-2,1'-isochromene] derivatives with generally excellent diastereoselectivity and good yields. A reasonable mechanism for forming these 6,6-dibenzannulated spiroketals involving 6-endo-dig oxo-cyclization and 1,6-addition-cyclization cascades is proposed.
View Article and Find Full Text PDFEnantioselective access to benzannulated spiroketals using a chiral sulfoxide auxiliary.
Org Biomol Chem
August 2013
School of Chemical Sciences, University of Auckland, 23 Symonds Street, Auckland 1142, New Zealand.
This article describes our efforts to develop an asymmetric synthesis of bisbenzannulated spiroketals using a chiral sulfoxide auxiliary. Our primary focus was on the synthesis of the 3H-spiro[benzofuran-2,2'-chroman] ring system, the spirocyclic core of the rubromycin family. Our strategy employed the use of lithium-halogen exchange on a racemic bromospiroketal in order to attach a chiral sulfoxide, thus producing two diastereomers.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!