ABSTRACT
The first synthesis of a pentacyclic ambiguine (ambiguine P) is reported. The synthesis takes advantage of sequential alkylations of an indole core to rapidly construct the pentacyclic framework of the natural product. Key to the success of the synthesis was the use of a Nicholas reaction to alkylate at C2, crafting a fused seven-membered ring that is characteristic of the pentacyclic ambiguines, as well as the use of an amide-directed functionalization at C12 to set a requisite quaternary center. A versatile late-stage intermediate was prepared that may be applicable to the synthesis of the other pentacyclic ambiguines.
Subject(s)
Indole Alkaloids/chemical synthesis , Alkylation , Amides/chemistry , Chemistry Techniques, SyntheticABSTRACT
Herein we describe the first approach to 3-oxidopyrylium ions from a linear precursor. Heating bis(1-cyanovinyl acetate) in the presence of a trace amount of pyridinium p-toluenesulfonate results in a series of acyl group transfers and an intramolecular cyclization event to form a 3-oxidopyrylium ion that can be trapped by reaction with several dipolarophiles. When treated with dienes, the result is a sequential [5 + 2]/[4 + 2] cycloaddition reaction that provides sp3-rich products of high molecular complexity.
Subject(s)
Heterocyclic Compounds, 3-Ring/chemistry , Vinyl Compounds/chemistry , Crystallography, X-Ray , Cyclization , Ions , Magnetic Resonance Spectroscopy , Molecular Structure , Pyridinium Compounds/chemistry , Spectrometry, Mass, Electrospray Ionization , Spectroscopy, Fourier Transform InfraredABSTRACT
We describe herein formal syntheses of the indole alkaloids cis-trikentrinâ A and herbindoleâ B from a common meso-hydroquinone intermediate prepared by a ruthenium-catalyzed [2+2+1+1] cycloaddition that has not been used previously in natural product synthesis. Key steps include a sterically demanding Buchwald-Hartwig amination as well as a unique C(sp(3) )-H amination/indole formation. Studies toward a selective desymmetrization of the meso-hydroquinone are also reported.
ABSTRACT
Tetralins (tetrahydronaphthalenes) are synthesised from benzocyclobutenols based on the rhodium-catalysed site-selective ring opening followed by intermolecular/intramolecular conjugate addition of the resulting arylrhodium species to electron-deficient alkenes. The produced structures make a remarkable contrast with those available from the same compounds under thermal reaction conditions.
Subject(s)
Cyclobutanes/chemistry , Polycyclic Compounds/chemistry , Rhodium/chemistry , Tetrahydronaphthalenes/chemistry , Catalysis , Molecular Structure , Tetrahydronaphthalenes/chemical synthesisABSTRACT
Carbon-carbon bonds constitute the major framework of organic molecules and carbon-hydrogen bonds are abundant in their peripheries. Such nonpolar σ-bonds are thermodynamically stable and kinetically inert in general. Nonetheless, selective activation of those ubiquitous bonds may offer a straightforward method to construct and/or functionalize organic skeletons. Herein we describe ring expansion from orthocyclophanes to metacyclophanes occurring upon sequential action of light and a metal catalyst. Formally, specific non-strained carbon-hydrogen and carbon-carbon bonds are cleaved and exchanged without elimination of any leaving groups. Notably, the product is energetically uphill from the starting material, but the endergonic photocyclization step makes it possible to drive the transformation forward. The ring expansion is extended to the stereospecific synthesis of metacyclophanes possessing planar chirality, during which central chirality on a tertiary carbon is transferred to planar chirality.
ABSTRACT
A rhodium catalyst induced ring opening of benzocyclobutenols with selective cleavage of the C(sp(2))-C(sp(3)) bond adjacent to the hydroxyl group. The site-selectivity markedly contrasted with that of their thermal ring-opening reaction. The rhodium-catalyzed ring opening led to the development of a new alkyne insertion reaction constructing a dihydronaphthalene framework.
Subject(s)
Cyclobutanes/chemistry , Ketones/chemical synthesis , Organometallic Compounds/chemistry , Rhodium/chemistry , Temperature , Catalysis , Ketones/chemistry , Molecular StructureABSTRACT
The rhodium-catalysed reaction of 1-(2-haloaryl)cyclobutanols afforded 3,3-disubstituted α-tetralones. The reaction was applied to the asymmetric synthesis of α-tetralones bearing a chiral quaternary carbon centre at the 3-position, which was otherwise difficult to execute.
