Progress toward the Synthesis of Garsubellin A and Related Phloroglucins: The Direct Diastereoselective Synthesis of the Bicyclo[3.3.1]nonane Core

A highly diastereoselective single-step cyclization reaction provides access to the bicyclo[3.3.1]nonane core of the polyprenylated phloroglucin natural product garsubellin A. Further elaboration to a more functionalized analogue involves a sequential Claisen rearrangement/Grubbs olefin cross-metathesis strategy. Additionally, this strategy was extended to the preparation of the bis-quaternary carbon array found at the bridgehead positions of the phloroglucin natural products

Asymmetric dearomatization/cyclization enables access to polycyclic chemotypes

Enantioenriched, polycyclic compounds were obtained from a simple acylphloroglucinol scaffold. Highly enantioselective dearomatization was accomplished using a Trost ligand-palladium(0) complex. A computational DFT model was developed to rationalize observed enantioselectivities and revealed a key reactant-ligand hydrogen bonding interaction. Dearomatized products were used in visible light-mediated photocycloadditions and oxidative free radical cyclizations to obtain novel polycyclic chemotypes including tricyclo[4.3.1.01,4]decan-10-ones, bicyclo[3.2.1]octan-8-ones and highly-substituted cycloheptanones.R24 GM111625 - NIGMS NIH HH

Punica granatum L.

https://thekeep.eiu.edu/herbarium_specimens_byname/20808/thumbnail.jp

A kinetic and theoretical study of the borate catalysed reactions of hydrogen peroxide: the role of dioxaborirane as the catalytic intermediate for a wide range of substrates

Our recent work has provided new insights into the equilibria and species that exist in aqueous solution at different pHs for the boric acid – hydrogen peroxide system, and the role of these species in oxidation reactions. Most recently, (M. C. Durrant, D. M. Davies and M. E. Deary, Org. Biomol. Chem., 2011, 9,7249–7254), we have produced strong theoretical and experimental evidence for the existence of a previously unreported monocyclic three membered peroxide species, dioxaborirane, that is the likely catalytic species in borate mediated electrophilic reactions of hydrogen peroxide in alkaline solution. In the present paper, we extend our study of the borate–peroxide system to look at a wide range of substrates that include substituted dimethyl anilines, methyl-p-tolyl sulfoxide, halides, hydrogen sulfide anion, thiosulfate ,thiocyanate, and hydrazine. The unusual selectivity–reactivity pattern of borate catalysed reactions compared with hydrogen peroxide and inorganic or organic peracids previously observed for theorganic sulfides (D. M. Davies, M. E. Deary, K. Quill and R. A. Smith, Chem.–Eur. J., 2005, 11, 3552–3558) is also seen with substituted dimethyl aniline nucleophiles. This provides evidence that the pattern is not due to any latent electrophilic tendency of the organic sulfides and further supports dioxaborirane being the likely reactive intermediate, thus broadening the applicability of this catalytic system. Moreover, density functional theory calculations on our proposed mechanism involving dioxaborirane are consistent with the experimental results for these substrates. Results obtained at high concentrations of both borate and hydrogen peroxide require the inclusion the diperoxodiborate dianion in the kinetic analysis .A scheme detailing our current understanding of the borate–peroxide system is presented

A Bryological Survey of Southwestern Nebraska

During the summer of 1982, moss collections made in Chase, Dundy. Frontier, Furnas, Gosper, Hayes, Hitchcock, Hooker, Lincoln, Logan. McPherson, Perkins, and Red Willow counties of Nebraska comprised 21 species. These reports bring the number of moss species known from southwestern Nebraska to 27 in addition to 5 liverwort species

A Bryological Survey of Southwestern Nebraska

During the summer of 1982, moss collections made in Chase, Dundy. Frontier, Furnas, Gosper, Hayes, Hitchcock, Hooker, Lincoln, Logan. McPherson, Perkins, and Red Willow counties of Nebraska comprised 21 species. These reports bring the number of moss species known from southwestern Nebraska to 27 in addition to 5 liverwort species

Total synthesis and absolute configuration assignment of MRSA active garcinol and isogarcinol

A short total synthesis of (±)-garcinol and (±)-isogarcinol, two endo-type B PPAPs with reported activity against methiciline resistant Staphylococcus aureus (MRSA), is presented. The separation of framework-constructing from framework-decorating steps and the application of two highly regio- and stereoselective Pd-catalysed allylations, that is, the Pd-catalysed decarboxylative Tsuji-Trost allylation and the diastereoselective Pd-catalysed allyl-allyl cross-coupling, are key elements that allowed the total synthesis to be accomplished within 13 steps starting from acetylacetone. After separation of the enantiomers the absolute configurations of the four natural products (i.e., (-)-garcinol, (+)-guttiferone E (i.e., ent-garcinol), (-)-isogarcinol, and (+)-isoxanthochymol (i.e., ent-isogarcinol)) were assigned based on ECD spectroscopy.Fil: Socolsky, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Quimica del Noroeste; Argentina. Universidad Nacional de Tucumán; ArgentinaFil: Plietker, Bernd . Universität Stuttgart. Institut für Organische Chemie; Alemani

Progress Toward the Total Synthesis of Garsubellin A and Structurally Related Phloroglucin Natural Products

Progress toward the polyprenylated phloroglucin garsubellin A is presented. A highly diastereoselective single-step cyclization reaction provides access to the bicyclo[3.3.1]nonane core of this natural product. Further elaboration to a more functionalized analog involves a sequential Claisen rearrangement/Grubbs olefin cross metathesis strategy. Additionally, the feasibility of this strategy toward the preparation of the bis-quaternary carbon array found at the bridgehead positions of the phloroglucinol natural products is demonstrated. Enantioselective strategies and model studies will also be discussed