Base-catalyzed intramolecular hydroamination of cyclohexa-2,5-dienes: insights into the mechanism through DFT calculations and application to the total synthesis of epi-elwesine.

The base-catalyzed intramolecular hydroamination of 1-ethylaminocyclohexa-2,5-dienes is described. The transformation proceeds through isomerization of the cyclohexa-1,4-dienyl fragment into the corresponding conjugated 1,3-diene prior to the hydroamination step. Attaching a chiral glycinol ether auxiliary on the amino group allows the protonation to occur with complete diastereocontrol. The resulting lithium amide then adds onto the 1,3-dienyl moiety, affording the desired fused pyrrolidine ring along with the corresponding lithium allylic anion. Protonation of the latter then proceeds with high regiocontrol to favor the resulting allylic amines. In contrast, when the reaction was performed on primary amines, fused pyrrolidines bearing a homoallylic amino group were obtained. The stereochemical course of the process and determination of the reaction pathways were established based on calculations performed at the DFT level. Finally, application of the methodology to the enantioselective synthesis of (+)-epi-elwesine, a crinane alkaloid, is described.

Salt-tolerance of alkyl-glyceryl ether carboxylates hydrotropes and surfactants. Dramatic effect of the methylation of the glyceryl spacer.

HYPOTHESIS: The insertion of polyether spacers between the anionic head and the alkyl chain of ionic surfactants significantly improves their salt-tolerance. The aim of this work is to study whether the petro-based polyethoxy spacer can be replaced by a glyceryl ether group for high salinity applications. EXPERIMENTS: A series of amphiphilic sodium salts of alkyl glyceryl ether carboxylates are synthesized with different alkyl chain lengths from 4 to 12 and various spacers between the glyceryl and the carboxylate groups. Their aggregation behavior is studied by tensiometry and their amphiphilicities are assessed by the PIT-slope method. The dramatic effect of the methylation of the glyceryl spacer on the salt-tolerance is highlighted, and rationalized by DFT calculations and molecular dynamics. FINDINGS: In contrast to the corresponding sodium soap, n-C6H13-CO2Na, and to the non-methylated counterpart, the sodium salt of 1-pentyl-3-methyl glyceryl ether methylene carboxylate ([5.0.1]-CH2CO2Na) exhibits an excellent salt-tolerance since it remains water-soluble with NaCl or CaCl2 concentrations greater than 20 wt% at 25 °C. Amphiphiles with short alkyl chains (

Birch reductive alkylation of biaryls: scope and limitations.

Birch reductive alkylation of biaryls has been carried out by varying the nature of the substituents on the aromatic rings. Our investigations have focused on electron-rich substituents such as OMe, OH, and NR(2) groups as they are present on the skeleton of targeted alkaloids. The regioselectivity is strongly affected by the electronic nature of these substituents on both rings. The 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and anilines do not react under these conditions. A biaryl possessing both a 3,5-dimethoxyphenyl moiety and a phenol ring may, however, be reduced and alkylated provided the acidic phenolic proton is removed prior to the treatment with Li in NH(3). Similarly, biaryls possessing a o-sulfonamide group are reduced regioselectively and alkylated with alpha-chloroacetonitrile or N-tosylaziridine to provide the corresponding dienes in reasonable to good yields. A survey of the alkylating agents was also performed showing that various functional groups may be introduced at the benzylic position, including esters, primary and tertiary amides, nitriles, epoxides, and acetals and also unfunctionalized sterically hindered t-Bu groups and cyclopropyl substituents. The introduction of the latter indicates that both a S(N)2 and a SET mechanism may take place during the alkylating step.

Desymmetrization of cyclohexa-2,5-dienes through a diastereoselective protonation-hydroamination cascade.

[reaction: see text] Intramolecular hydroamination of cyclohexa-2,5-dienes led with high selectivity to the corresponding bicyclic allylic amines. This study demonstrates that the reaction does not proceed through a direct hydroamination of one of the diastereotopic olefins but more likely involves a diastereoselective protonation of a pentadienyl anion, followed by addition of a lithium amide across the double bond of the resulting 1,3-diene, and is concluded by a highly regioselective protonation of the final allylic anion.

Total Synthesis of Putative 11-epi-Lyngbouilloside Aglycon.

We report here the total synthesis of 11-epi-lyngbouilloside aglycon. Our strategy features a Boeckman-type esterification followed by a RCM to form the 14-membered ring macrolactone and a late-stage side chain introduction via a Wittig olefination. Overall, the final product was obtained in 20 steps and 2% overall yield starting from commercially available 3-methyl-but-3-enol. Most importantly, the strategy employed is versatile enough to eventually allow us to complete the synthesis of the natural product and irrevocably confirm its structure.

Regioselectivity of Birch reductive alkylation of biaryls.

[reaction: see text] The regioselectivity of the Birch reductive alkylation of polysubstituted biaryls has been investigated. Results indicate that regioselectivity is affected by the electronic nature of substituents on both aromatic rings. The electron-rich 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and aniline are not dearomatized under these conditions. Biaryls possessing a phenol moiety are alkylated on the second ring, providing that the acidic proton has been removed prior to the Li/NH3 reduction.

Dramatic synergistic effects between hydroquinone and resorcinol derivatives for the organocatalyzed reduction of dioxygen by diethylhydroxylamine.

Diethylhydroxylamine reduces dioxygen in the presence of catalytic amounts of hydroquinone. A great improvement is achieved by adding resorcinol derivatives as co-catalysts. Though the formation of heterodimers does not seem to be the sole cause of the synergy, such products constitute a new class of powerful organocatalysts for dioxygen scavenging.

Lyngbouilloside and related macrolides from marine cyanobacteria.

Lyngbouilloside and the related macrolides lyngbyaloside, lyngbyaloside B and lyngbyaloside C have attracted a lot of attention over the past decade due to their intriguing architecture, their natural scarcity and their potential biological activities. This review aims to showcase the various strategies that have been used to access these natural products.

Total synthesis of nominal lyngbouilloside aglycon.

The first enantioselective total synthesis of the originally assigned structure of lyngbouilloside aglycon has been achieved using a particularly flexible route featuring an acylketene macrolactonization of a tertiary methyl carbinol as the key step. Comparison of the C13 chemical shifts of our synthetic aglycon with the ones pertaining to natural lyngbouilloside and lyngbyaloside C resulted in a possible stereochemical reassignment of the C11 stereogenic center.

Straightforward assembly of the octahydroisoquinoline core of morphinan alkaloids.

The octahydroisoquinoline core of morphinan was assembled starting from readily available arylcyclohexadienes. Three different approaches were developed, including a metal- and an acid-mediated Mannich type process and an anionic-mediated cyclization. All provided the desired motif as a single diastereomer having a C9-C13-C14 trans-cis relative configuration.

Straightforward synthesis of the near-infrared fluorescent voltage-sensitive dye RH1691 and analogues thereof.

A highly straightforward synthesis of the near-infrared voltage-sensitive dye RH1691 is reported featuring two sequential anionic additions of C-nucleophilic heterocycles on a cyanine. This convergent approach led to the synthesis of four new probes, which also exhibit fluorescence in the near-infrared region.

Palladium-catalyzed C-allylation of benzoins and an NHC-catalyzed three component coupling derived thereof: compatibility of NHC- and Pd-catalysts.

A large range of benzoins was successfully applied as C-nucleophiles in the palladium-catalyzed allylic alkylation with several allyl acetates, resulting in functionalized tertiary homoallylic alcohols. A number of unsymmetrical benzoins can be coupled with high levels of regio- and chemoselectivity. Finally, the challenging compatibility of free N-heterocyclic carbenes with a palladium catalyst has been utilized in a number of metal- and organocatalyzed three-component coupling reactions.