Construction of macrocyclic thiodepsipeptides: synthesis of a nosiheptide 'southern hemisphere' model system

A 20-membered macrocyclic thiodepsipeptide has been synthesized as a model for the southern hemisphere of nosiheptide, the key steps being assembly of an acyclic precursor by amide coupling of indole and thiazole fragments followed by formation of the thiolactone in the macrocyclization step

Solar Photochemical Oxidation of Alcohols using Catalytic Hydroquinone and Copper Nanoparticles under Oxygen: Oxidative Cleavage of Lignin Models

Alcohols are converted into to their corresponding carbonyl compounds using catalytic amounts of 1,4-hydroquinone with a copper nanoparticle electron transfer mediator with oxygen as the terminal oxidant in acetone as solvent under visible light irradiation. These conditions employing biorenewable hydroquinone as reagent were developed from initial experiments using stoichiometric amounts of 1,4-benzoquinone as oxidant. A range of benzylic and aliphatic primary and secondary alcohols are oxidized, affording the corresponding aldehydes or ketones in moderate to excellent yields. The methodology is also applicable to the oxidative degradation of lignin model compounds that undergo C–C bond cleavage to give simple aromatic compounds

Two-Step Route to Indoles and Analogues from Haloarenes: A Variation on the Fischer Indole Synthesis

In a new variation on the Fischer indole synthesis, readily available haloarenes are converted into a wide range of indoles in just two steps by halogen–magnesium exchange and quenching with di-<i>tert</i>-butyl azodicarboxylate, followed by reaction with aldehydes or ketones under acidic conditions. The protocol, which is readily extended to the preparation of indole isosteres, 4- and 6-azaindoles and thienopyrroles, obviates the need to prepare potentially toxic aryl hydrazines, simultaneously avoiding undesirable anilines such as naphthylamines

A New Route to α‑Carbolines Based on 6π-Electrocyclization of Indole-3-alkenyl Oximes

Indoles are converted into α-carbolines in four steps by acylation at C-3, Boc-protection, olefination of the resulting 3-indolyl aldehydes or ketones to give <i>N</i>-Boc-3-indolyl alkenyl oxime <i>O</i>-methyl ethers, which upon heating to 240 °C under microwave irradiation undergo loss of the Boc-group, and 6π-electrocyclization to α-carbolines, following aromatization by loss of methanol (11 examples, 30–90% yield)

Toward the Total Synthesis of Hygrocin B and Divergolide C: Construction of the Naphthoquinone–Azepinone Core

A highly regioselective Diels–Alder approach toward the bioactive natural products hygrocin B and divergolide C is presented. The route uses an unusual benzoquinone–azepinone dienophile prepared in 8 steps from ethyl 8-methoxy-1-naphthoate, by a route which includes, as key steps, a Birch alkylation and a Beckmann rearrangement of a tetralone oxime, both of which are demonstrated on multigram scale. The naphthoquinone–azepinone core is suitably functionalized for addition of the ansa-chain, found in the natural products

Synthesis and electrochemical properties of the naturally occurring free radical scavenger carazostatin

A short synthesis of the naturally occurring free radical scavenger carazostatin 1 starting from indol-3-ylacetic acid is described, the key step being the regiospecific Diels–Alder reaction of the indolopyrone 2 with ethyl trimethylsilylpropynoate. Electrochemical studies on carazostatin and some of its derivatives show it to be more easily oxidised than butylated hydroxytoluene (BHT)

Solar Photochemical Oxidations of Benzylic and Allylic Alcohols Using Catalytic Organo-oxidation with DDQ: Application to Lignin Models

Visible light has a dramatic effect on the oxidation of benzylic and allylic alcohols, including those deactivated by electron-withdrawing groups, and β-O-4 lignin models, using catalytic amounts of the organo-oxidant 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Sodium nitrite or <i>tert</i>-butyl nitrite is used as cocatalyst, and oxygen is employed as the terminal oxidant

Biomimetic Synthesis of the Apoptosis-Inducing Thiazinoquinone Thiaplidiaquinone A

A concise total synthesis of the apoptosis-inducing, marine metabolite thiaplidiaquinone A is described. The key ring forming steps are both based on biosynthetic considerations and involve the construction of the central benzo­[<i>c</i>]­chromene quinone unit by an extremely facile oxa-6π-electrocyclic ring closure reaction of an <i>ortho</i>-quinone intermediate, derived by tautomerization of a bis-benzoquinone, readily accessed from two simple phenolic precursors. This is followed by the installation of the 1,4-thiazine-dioxide ring by reaction of the benzo­[<i>c</i>]­chromene quinone with hypotaurine

Total Synthesis of (±)-Distomadines A and B

The total synthesis of distomadines A and B, two structurally unique tetracyclic quinolines, is described. The route features a three-step process to access the pyranoquinoline butenolide rings via a Suzuki cross coupling of a 5-bromo-4-methoxycarbonylmethoxyquinoline with a vinyl boronate, followed by an α-ketohydroxylation and double cyclization by intramolecular aldol condensation and lactonization. Subsequent manipulation of the side chain to introduce the guanidine fragment completed the synthesis of distomadine B, whereas the distomadine A congener resulted from decarboxylation of a late-stage intermediate

Two Approaches to the Aromatic Core of the Aminonaphthoquinone Antibiotics

Two complementary approaches are presented for the synthesis of the quinone chromophores of the naphthoquinone ansamycins and related natural products. The first involves the use of an improved protocol for the manganese­(III) acetate mediated cyclization of 5-aryl-1,3-dicarbonyl compounds to β-naphthols, leading to the simple, scalable preparation of building blocks suitable for the synthesis of naturally occurring aminonaphthoquinones. The second approach involves the Diels–Alder reaction of a series of new, ester-containing Danishefsky-type dienes with <i>N</i>-protected aminobenzoquinones to allow more expeditious access to similar intermediates