A General and Versatile Method for CC Cross-Coupling Synthesis of Conjugated Enynes: One-Pot Sequence Starting from Carbonyl Compounds

The LANCA three-component reaction to highly substituted β-ketoenamides - versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

The LANCA three-component reaction of lithiated alkoxyallenes LA, nitriles N and carboxylic acids CA leads to β-ketoenamides KE in good to excellent yields. The scope of this reaction is very broad and almost all types of nitriles and carboxylic acids have successfully been used. The alkoxy group introduced via the allene component is also variable and hence the subsequent transformation of this substituent into a hydroxy group can be performed under different conditions. Enantiopure nitriles or carboxylic acids can also be employed leading to chiral KE with high enantiopurity and dinitriles or dicarboxylic acids also lead to the expected bis-β-ketoenamides. β-Ketoenamides incorporate a unique combination of functional groups and hence a manifold of subsequent reactions to highly substituted heterocyclic compounds is possible. An intramolecular aldol-type condensation reaction efficiently furnishes pyridin-4-ols PY that can be further modified by palladium-catalyzed reactions, e.g., to specifically substituted furopyridine derivatives. Condensations of β-ketoenamides with ammonium salts or with hydroxylamine hydrochloride afford pyrimidines PM or pyrimidine N-oxides PO with a highly flexible substitution pattern in good yields. The functional groups of these heterocycles also allow a variety of subsequent reactions to various pyrimidine derivatives. On the other hand, acid-labile alkoxy substituents such as a 2-(trimethylsilyl)ethoxy group are required for the conversion of β-ketoenamides into 5-acetyl-substituted oxazoles OX, again compounds with high potential for subsequent functional group transformations. For acid labile β-ketoenamides bearing bulky substituents the acid treatment leads to acylamido-substituted 1,2-diketones DK that could be converted into quinoxalines QU. All classes of heterocycles accessed through the key β-ketoenamides show a unique substitution pattern - not easily accomplishable by alternative methods - and therefore many subsequent reactions are possible.

Aqueous Sonogashira coupling of aryl halides with 1-alkynes under mild conditions: use of surfactants in cross-coupling reactions

Aqueous solutions of common and inexpensive surfactants (e.g. SDS and CTAB) are surveyed as an alternative to organic solvents in Sonogashira cross-coupling. Aryl-bromide substrates are best coupled under Cu-free conditions.

Total synthesis of myceliothermophins C, D, and E

The total synthesis of cytotoxic polyketides myceliothermophins E (1), C (2), and D (3) through a cascade-based cyclization to form the trans-fused decalin system is described. The convergent synthesis delivered all three natural products through late-stage divergence and facilitated unambiguous C21 structural assignments for 2 and 3 through X-ray crystallographic analysis, which revealed an interesting dimeric structure between its enantiomeric forms.

Catalytic asymmetric synthesis of 1,3-enyne scaffolds: design and synthesis of conjugated nitro dienynes as novel Michael acceptors and development of a new synthetic methodology

A catalytic enantioselective synthesis of 1,3-enynes for the development of nitro dienynes as novel Michael acceptors has been developed.

Total synthesis and stereochemical revision of the chlorinated sesquiterpene (±)-gomerone c

Revised: the total synthesis of gomerone C results in revision of the stereochemical assignment at C3. The synthetic strategy relies on a late-stage Conia-ene reaction, which efficiently forms the bicyclo[3.2.1]octane containing the bridgehead chloride and generates an exocyclic olefin, which can be used as a flexible handle for further elaboration. The two contiguous quaternary centers are installed by means of a Diels-Alder reaction.

First Comprehensive Investigation of Suzuki Couplings of Alkenyl Nonaflates with Aryl and Alkenyl Boronic Acid Derivatives by Using Classical Conditions and Microwave Heating

Alkenyl nonaflates (nonafluorobutanesulfonates) are excellent substrates in a variety of palladium-catalysed coupling reactions. We herein demonstrate that bicyclic nonaflates generated from 8-heterobicyclo[3.2.1]octan-3-one derivatives can be coupled with aryl or alkenyl boronic acids in a very efficient manner. The resulting densely functionalised bicyclic skeletons are highly suitable for further synthetic elaboration. The thermal Suzuki couplings provided the expected products in moderate to good yields. Microwave (MW) irradiation dramatically shortened reaction times and gave superior results. Bisboronic ester 19 was also coupled with bicyclic nonaflates, for example, with 14, and double Suzuki-coupling products, such as 22, were isolated in good yields. We demonstrated the great synthetic potential of aryl-substituted 8-heterobicyclo[3.2.1]octene derivatives, such as 15, by the stereoselective conversion of this compound into highly substituted furanose 31 or substituted pyran derivative 33, which were obtained in short and efficient reaction sequences.