A Novel Approach Towards Dibenzylbutyrolactone Lignans Involving Heck and Radical Reactions: Application to (±)-Matairesinol Synthesis

Asymmetric total synthesis of diosniponols A and B

A concise asymmetric total synthesis of diosniponols A and B has been achieved based on an enantioselective Jacobsen kinetic resolution of racemic epoxide and the important 2,3-dihydro-4H-pyran-4-one moiety being installed by the metal-free δ-hydroxyalkynone rearrangement catalyzed by p-TsOH. A diastereoselective catalytic hydrogenation set the required all-syn stereochemistry leading to diosniponol A, which then, under the Mitsunobu inversion conditions, provided diosniponol B. The structure and absolute stereochemistry of the natural products were further confirmed.

Total Synthesis of Lamellarins U and A3 by Interrupting Halogen Dance

A total synthesis of lamellarins U and A3 is described. The synthesis features the interruption of a halogen dance reaction of a metalated α,β-dibromopyrrole. The pyrrolylmagnesium reagent, generated by deprotonative metalation by using (TMP)MgCl·LiCl (TMP = 2,2,6,6-tetramethylpiperidide) as the base, was transmetalated to the corresponding organozinc species without causing the halogen dance reaction, which underwent a Negishi coupling to incorporate an aryl group onto the pyrrole ring. The arylated α,β-dibromopyrrole was then converted into lamellarins U and A3 through an α-selective halogen–magnesium exchange followed by carboxylation and subsequent palladium-mediated cyclization. The late-stage introduction of another aryl group was performed using a Kosugi–Migita–Stille coupling to provide lamellarins U and A3.

Reactions of Styrylmalonates with Aromatic Aldehydes: Detailed Synthetic and Mechanistic Studies

Reactions of styrylmalonates with aromatic aldehydes in the presence of Lewis and Brønsted acids and their regularities have been studied in detail. Approaches to the synthesis of various polysubstituted 5,6-dihydropyran-2-ones, indenes, aryl-containing dienes and trienes, cyclopentadienes, and polycyclic lactones have been developed with chemo-, regio-, stereo-, and diastereoselectivity control. The mechanisms of these reactions were studied in depth using multinuclear NMR experiments, monitoring the reactions in the NMR tube, and ¹⁸O isotope labeling.

Synthesis of Substituted β-Styrylmalonates by Sequential Isomerization of 2-Arylcyclopropane-1,1-dicarboxylates and (2-Arylethylidene)malonates

A method has been developed for the synthesis of substituted β-styrylmalonates by conversion of 2-arylcyclopropane-1,1-dicarboxylates (ACDCs) in the presence of gallium trichloride into the corresponding­ 1,2-zwitterionic intermediates or (2-arylethyl­idene)malonates, followed by treatment with pyridine at room temperature leading to an isomerization of the emerging double bond. This method allows one to expand these reactions to include ACDCs with acceptor substituents at the aromatic ring.

Reagents that Contain Se-H or Te-H Bonds

Species that contain bonds between hydrogen and selenium or tellurium have a characteristic high reactivity, which can be harnessed in the synthesis of valuable organic compounds. This overview includes the synthesis of dihydrides, alkali metal hydrochalcogenides, chalcogenols, chalcogenocarboxylic and chalcogenocarbamic acids, and their application in reactions of reduction, addition to unsaturated compounds, and nucleophilic substitution.

Stereospecific Synthesis of α-Amino Allylsilane Derivatives through a [3,3]-Allyl Cyanate Rearrangement. Mild Formation of Functionalized Disiloxanes

An efficient asymmetric synthesis of α-amino allylsilane derivatives is reported. The strategy is based on a [3,3]-allyl cyanate sigmatropic rearrangement from enantioenriched γ-hydroxy alkenylsilyl compounds. The isocyanate intermediate can be trapped by several nucleophiles, opening the way for the preparation of unknown chiral functionalized compounds such as the α-ureido allylsilanes as well as carbamate derivatives. A computational study was conducted to rationalize the complete 1,3-chirality transfer of this kind of rearrangement. Moreover, starting from products bearing a phenyldimethyl silyl substituent, the α-amino silane derivatives or the corresponding disiloxanes can be obtained under hydrogenation conditions in an exclusive way according to the used catalyst.

Synthesis of aminomethyl derivatives of 5-substituted-3-(prop-2-ynyl)dihydrofuran-2(3H)-ones

An easy approach for the synthesis of various 5-substituted-3-(prop-2-ynyl)dihydrofuran-2(3H)-ones is described. As a method of choice, Mannich aminomethylation of terminal alkynes is adopted. The reaction works well with acyclic and cyclic secondary amines and provides the desired products, with good to very good yields.

Synthesis of Neurotrophic Seco-prezizaane Sesquiterpenes (1R,10S)-2-Oxo-3,4-dehydroneomajucin, (2S)-Hydroxy-3,4-dehydroneomajucin, and (-)-Jiadifenin

An asymmetric approach to the synthesis of neurotrophic seco-prezizaane sesquiterpenes is described that is based on the strategic application of a hydroxyl-directed metallacycle-mediated [2 + 2 + 2] annulation and an intramolecular radical cyclization cascade. Targets prepared are among the most potent members of the natural product class and include (1R,10S)-2-oxo-3,4-dehydroneomajucin, (2S)-hydroxy-3,4-dehydroneomajucin, and (-)-jiadifenin. In addition to representing the first application of the alkoxide-directed metallacycle-mediated hydrindane-forming annulation reaction in natural product synthesis and the first total synthesis of (2S)-hydroxy-3,4-dehydroneomajucin, these pursuits have resulted in the elucidation of a complex radical cascade process for installation of the C5 quaternary center common to the natural product class.

Synthesis of highly functionalized [3]dendralenes and their Diels–Alder reactions displaying unexpected regioselectivity

Sequential olefinations were applied for the synthesis of acyclic tetrasubstituted [3]dendralenes, which did not cyclodimerize and displayed unusual regioselectivity in the Diels–Alder reaction.

Pd(II)-SDP-catalyzed enantioselective 5-exo-dig cyclization of γ-alkynoic acids: application to the synthesis of functionalized dihydofuran-2(3H)-ones containing a chiral quaternary carbon center

The Pd(II)-SDP-catalyzed first enantioselective intramolecular cyclization of α,α-disubstituted γ-alkynoic acids is described. This 5-exo-dig cyclization afforded dihydrofuran-2(3H)-ones bearing a chiral quaternary carbon center in excellent yields with enantioselectivities up to 71%. A mechanism involving palladium(II) species is proposed to rationalize the outcome of the reaction.

Iridium-catalyzed (Z)-trialkylsilylation of terminal olefins

A complex of commercial [Ir(OMe)(cod)](2) and 4,4-di-tert-butyl-2,2-bipyridine (dtbpy) catalyzes the Z-selective, dehydrative silylation of terminal alkenes, but not 1,2-disubstituted alkenes, with triethylsilane or benzyldimethylsilane in THF at 40 degrees C. Yields and Z-stereoselectivity were significantly improved by 2-norbornene, in contrast with other sacrificial alkenes. The reaction is compatible with many functional groups including epoxides, ketones, amides, alcohols, esters, halides, ketals, and silanes. alpha,beta-Unsaturated esters were unreactive. The reaction probably proceeds through a Heck-type mechanism.