Papers by Richmond Sarpong
Journal of the American Chemical Society, Jun 4, 2012
A W(CO)(5)·THF-catalyzed cycloisomerization of bicyclo[4.1.0] substrates to afford mono C4-substi... more A W(CO)(5)·THF-catalyzed cycloisomerization of bicyclo[4.1.0] substrates to afford mono C4-substituted 4,5-dihydro-benzo[b]furans and -indoles is reported. The title compounds are versatile intermediates that lead to a range of fused bicycles including the cores of various furan-, benzofuran-, and indole-containing natural products. In many cases, the functionalization of the dihydro-benzo[b]furans and -indoles is orthogonal to that of the corresponding benzofurans and indoles and, thus, offers complementary approaches for synthesis.
Organic Letters, 2015
An approach to construct enantiopure complex natural product-like frameworks, including the first... more An approach to construct enantiopure complex natural product-like frameworks, including the first reported synthesis of a C17 oxygenated taxoid scaffold, is presented. A palladium-catalyzed C-C activation/cross-coupling is utilized to access these structures in a short sequence from (+)-carvone; the scope of this reaction is explored.
Angewandte Chemie International Edition
ABSTRACT
Journal of the American Chemical Society, Jan 19, 2015
The continued development of transition metal-mediated C-C bond activation/cleavage methods would... more The continued development of transition metal-mediated C-C bond activation/cleavage methods would provide even more opportunities to implement novel synthetic strategies. We have explored the Rh(I)-catalyzed C-C activation of cyclobutanols resident in hydroxylated derivatives of pinene, which proceed in a complementary manner to the C-C bond cleavage which we have observed with many traditional electrophilic reagents. Mechanistic and computational studies have provided insight into the role of C-H activation in the stereochemical outcome of the Rh-catalyzed C-C bond activation process. Using this new approach, functionalized cyclohexenones that form the cores of natural products including the spiroindicumides and phomactin A have been accessed.
Chem. Commun., 2015
Substituted piperidines are emerging as important medicinally-active structural motifs. Here, we ... more Substituted piperidines are emerging as important medicinally-active structural motifs. Here, we report highly stereoselective carbolithiation reactions of α-aryl piperidine enecarbamates that offer direct access to vicinally-substituted piperidine compounds. We have also demonstrated that the carbanion intermediates can be trapped with a carbon electrophile.
Tetrahedron Letters, 2015
A possible biosynthetic link between atropurpuran, the hetidine diterpenoid alkaloids and the alk... more A possible biosynthetic link between atropurpuran, the hetidine diterpenoid alkaloids and the alkaloid arcutine and congeners is proposed. The feasibility of aspects of this biosynthesis, especially key 1,2-rearrangements, have been examined computationally.
Organic Letters, 2012
Carbonylimidazole derivatives have been found to be highly active acylation reagents for esterifi... more Carbonylimidazole derivatives have been found to be highly active acylation reagents for esterification and amidation in the presence of pyridinium salts. These reactions are thought to involve both Brønsted acid and nucleophilic catalysis. This mode of activation has been applied to the synthesis of difficult to access oxazolidinones, as well as esters and amides. Finally, the use of pyridinium salts has been shown to accelerate the esterification of carboxylic acids with imidazole carbamates.
Tetrahedron Letters, 2002
A synthesis of a simple trans fused [8.3.0]bicyclic enediyne framework was developed from cyclope... more A synthesis of a simple trans fused [8.3.0]bicyclic enediyne framework was developed from cyclopentanone-trans-3,4-dicarboxylate. The rates of rearrangement of several derivatives of the framework were measured, and correlated with structural features. Preliminary studies to adjust the configuration about the ring fusion, expected to be an activation step, are discussed.
Tetrahedron, 2011
The optimization, substrate scope, and mechanism of esterification and amidation of carboxylic ac... more The optimization, substrate scope, and mechanism of esterification and amidation of carboxylic acids mediated by imidazole-based reagents are discussed. The innate reactivity of carbonylimidazole reagents with a range of nucleophiles is also explored. New reagents developed for the synthesis of α,β-unsaturated esters are described, as are reagents for the preparation of tertiary amides directly from carboxylic acids.
Organic Letters, 2010
Imidazole carbamates and ureas were found to be chemoselective esterification and amidation reage... more Imidazole carbamates and ureas were found to be chemoselective esterification and amidation reagents. A wide variety of carboxylic acids were converted to their ester or amide analogues by a simple synthetic procedure in high yields.
Organic Letters, 2013
The core architecture of the citrinadin alkaloids has been prepared in racemic form by utilizing ... more The core architecture of the citrinadin alkaloids has been prepared in racemic form by utilizing a strategy that exploits the alkylation of 2-methoxypyridines. An initially planned indolizidine to quinolizidine transformation to build the D/E rings was unsuccessful. Success was ultimately gained by a direct alkylation to establish the citrinadin core architecture.
Organic Letters, 2014
The synthesis of functionalized azepanes was accomplished through the palladium-mediated cross-co... more The synthesis of functionalized azepanes was accomplished through the palladium-mediated cross-coupling of α-halo eneformamides with mostly unactivated nucleophiles under mild conditions. Alkenylations proceeded with excellent stereoselectivitiy. In most cases, high yields of the coupling products were obtained.
Nature, 2014
Many natural products that contain basic nitrogen atoms--for example alkaloids like morphine and ... more Many natural products that contain basic nitrogen atoms--for example alkaloids like morphine and quinine-have the potential to treat a broad range of human diseases. However, the presence of a nitrogen atom in a target molecule can complicate its chemical synthesis because of the basicity of nitrogen atoms and their susceptibility to oxidation. Obtaining such compounds by chemical synthesis can be further complicated by the presence of multiple nitrogen atoms, but it can be done by the selective introduction and removal of functional groups that mitigate basicity. Here we use such a strategy to complete the chemical syntheses of citrinalin B and cyclopiamine B. The chemical connections that have been realized as a result of these syntheses, in addition to the isolation of both 17-hydroxycitrinalin B and citrinalin C (which contains a bicyclo[2.2.2]diazaoctane structural unit) through carbon-13 feeding studies, support the existence of a common bicyclo[2.2.2]diazaoctane-containing biogenetic precursor to these compounds, as has been proposed previously.
Journal of the American Chemical Society, 2010
The total synthesis of the Lycopodium alkaloid complanadine A, which is an unsymmetrical dimer of... more The total synthesis of the Lycopodium alkaloid complanadine A, which is an unsymmetrical dimer of lycodine, was achieved by exploiting a common tetracyclic precursor. Key to the success of the synthesis was the development of a late-stage site-selective C-H functionalization of a pyridine moiety to arrive at a key boronic ester intermediate.
Chemical Research in Toxicology, 2012
Radiolabeled anthranilic diamide insecticide [N-C(3)H(3)]chlorantraniliprole was synthesized at h... more Radiolabeled anthranilic diamide insecticide [N-C(3)H(3)]chlorantraniliprole was synthesized at high specific activity. It was compared with phthalic diamide insecticide flubendiamide and [(3)H]ryanodine in radioligand binding studies with house fly muscle membranes to provide the first direct evidence with a native insect ryanodine receptor that the major anthranilic and phthalic diamide insecticides bind at different allosterically coupled sites, i.e., there are three distinct Ca(2+)-release channel targets for insecticide action.
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Papers by Richmond Sarpong