The first reverse regioselective intermolecular annulation of aryl substituted 2-acetylenic ketones with O-substituted N-hydroxybenzamides or acrylamides followed by tandem cyclization via ruthenium-catalyzed C–H activation, is reported.
The first synthesis of dolabelide C (1), a cytotoxic marine macrolide, is reported utilizing a phosphate tether-mediated approach. Bicyclic phosphates (S,S,SP)-5 and (R,R,RP)-5 serve as the central building blocks for the construction of two major 1,3-anti-diol subunits in 1 through selective cleavage pathways, regioselective olefin reduction and cross-metathesis. Overall, phosphate-mediated processes provided copious amounts of both major subunits allowing for a detailed RCM macrocyclization study to the 24-membered macrolactone 1.
A mild and efficient Pd-catalyzed arylative domino carbocyclization of cyclohexadienone-containing 1,6-enynes is described. The reaction tolerates a variety of functionalized boronic acids to afford a cis-fused bicyclic framework containing an α,β-unsaturated ketone with excellent regio- and diastereoselectivity in good yields. The tandem process proceeds with β-arylation of propargylic ether followed by conjugate addition of a vinyl palladium intermediate and subsequent protonolysis of a palladium enolate.
An efficient synthesis of (−)-tetrahydrolipstatin (THL) is reported. This method takes advantage of a phosphate tether-mediated, one-pot, sequential RCM/CM/hydrogenation protocol to deliver THL in 8 total steps from a readily prepared (S,S)-triene. The strategy incorporates selective cross metathesis, regio-selective hydrogenation, regio-and diastereoselective cuprate addition and Mitsunobu inversion for installation of the C5 formamide ester subunit.(−)-Tetrahydrolipstatin (THL, 1) is an anti-obesity drug marketed under generic name Orlistat ® and is a stable saturated form of the naturally occuring lipstatin (2) (Figure 1). Lipstatin is a protein-reactive natural product and an irreversible pancreatic lipase inhibitor which was first isolated in 1987 from Streptomyces toxytricini. 1 The biological activity inherent to this family of molecules is based on the reactivity of the β-lactone moiety which is readily acylated by the pancreatic lipase enzyme. This process ultimately inhibits the enzyme reactivity aimed at hydrolyzing triglycerides to produce free fatty acids which are then readily absorbed into the dietary system. 1b,2 Recently, the discovery of selective inhibition of thioesterase activity of fatty acid synthase (FAS) in cancer cells has elevated the potential of Orlistat ® as an anticancer drug. 3,4 The inhibition of FAS stops both endothelial cell proliferation and angiogenesis and ultimately delays tumor progression in a variety of cancer cells. This promising activity highlights the broad and interesting biological profile of Orlistat ® and has prompted renewed synthetic efforts and corresponding biology of THL, lipstatin and analogs thereof.4 ,5 Herein we report a concise total synthesis of (−)-tetrahydrolipstatin via a strategy utilizing a phosphate-tether-mediated, one-pot, sequential RCM/CM/hydrogenation pathway of triene (S,S)-7. 6 Overall, the reported phanson@ku.edu. Supporting Information Available Experimental details and spectroscopic data of new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.
NIH Public Access Author ManuscriptOrg Lett. Author manuscript; available in PMC 2011 April 2.
NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript synthetic route comprises 9 total steps from the readily prepared diene diol-(S,S)-8 and highlights the utility of phosphate tethered processes and one-pot, multi-step operations.The first total synthesis of THL was achieved in 1987 by Schneider and coworkers utilizing Wittig olefination and an aldol condensation as key steps in a non-stereoselective process.7 Numerous total syntheses,8 formal syntheses 9 and synthetic analogues have followed this initial report, with the majority of synthetic pathways comprised of 14-25 steps. The shortest routes to THL reported to-date range from 10-12 steps using an array of synthetic strategies, including, (i) a 12-step anti-aldol approach,8i (ii) a 12-step diastereoselective allylation and crotylation sequence utilizing allyl/crotyltri...
A novel insertion reaction of N-tosylacetimidates and N-tosylacetimidamides onto arynes via a benzocyclobutene intermediate followed by ring cleavage is developed to afford o-benzylbenzoic acid derivatives in good yields. Interestingly, the use of cyclic 2-sulfonyliminoindolines provided two distinct products such as azepanimines via [2 + 2] cycloaddition and indolamines via protonation based on solvent medium.
The highly efficient and expedient route for the syntheses of 2-aroyl benzofurans has been developed via the cascade [2+2] followed by a [4+1] annulation on arynes. The overall transformation proceeded through the formation of ortho-quinone methide by the insertion of transient aryne into N, N-dimethylformamide and subsequent trapping with sulfur ylide. Moreover, this transformation has a broad range of substrate scope with a high functional-group tolerance. This new reaction was successfully utilized in the synthesis of the potent CYP19 aromatase inhibitor and late-stage functionalization on the bioactive complex estrone.
A versatile three-step, one-pot, sequential reaction protocol involving RCM, CM, and chemoselective hydrogenation is reported. This phosphate tether-mediated process occurs without intermediate isolation, is chemoselective and is governed by stereoelectronic properties innate to phosphate tethers, which ultimately act to preserve the integrity of the bisallylic, bicyclic phosphate for subsequent nucleophilic additions. Overall, this process can be used to efficiently generate advanced polyol synthons.
Rhodium-catalyzed
asymmetric hydrogenation of alkyne-tethered cyclohexadienones
enables highly regio- and enantioselective reductive cyclization to
afford cis-hydrobenzofurans and cis-hydroindoles in high yields. Desymmetrization of 1,3-diyne-tethered
cyclohexadienones was also explored, wherein the intramolecular coordination
of a Rh complex with the cyclohexadienone ring induces exclusive regioselectivity.
Mechanistic studies including hydrogen–deuterium crossover
experiments suggested that hydrogen activation is the rate-determining
step for tandem reductive cyclization. Moreover, this highly practical
and atom-economical transformation has tolerance to many functional
groups with a broad range of substrate scope, allowing further transformations
to expand the structural complexity of the bicyclic scaffolds.
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