Synthesis of Desacyl Furanmonogones A and B

Asymmetric Total Synthesis of Janthinoid A

The asymmetric total synthesis of janthinoid A has been accomplished for the first time in 14 steps without using a protecting group. The trans-decalin subunit and the rigid oxabicyclo[3.2.1]octane motif were constructed via an epoxide-initiated cationic π-cyclization reaction and a Fe(ClO4)3-mediated oxidative cascade cyclization reaction, respectively.

Isolation and Biomimetic Semisynthesis of Hyperzrones A and B, Two Nor-Polycyclic Polyprenylated Acylphloroglucinols with a Characteristic Cyclobutane Moiety, from Hypericum beanii

Hyperzrones A (1) and B (2), two unprecedented nor-polycyclic polyprenylated acylphloroglucinols with a characteristic cyclobutane moiety, were discovered from Hypericum beanii. Their structures were determined by extensive spectroscopic analysis, X-ray crystallography, and quantum chemical calculation methods. A bioinspired semisynthesis of 1 and 2 was achieved from the natural precursor hypercalin B (3), featuring a Favorskii-type rearrangement and a visible-light-mediated [2 + 2] photocycloaddition. Several diverse derivatives were also obtained, providing a compound library for biological studies.

Ferrocene-Mediated Electrochemical Polycyclization of Malonates

We report access to the core of biologically relevant aromatic abietane diterpenoids and to the formal synthesis of podocarpic and lambertic acids or γ-lactones via an electrochemical bicyclization process initiated by the ferrocene-mediated anodic oxidation of a malonate via single electron-transfer. This approach permits escaping the use of excess of oxidants such as Mn(OAc)3 and the associated complicated purification.

Multicomponent Synthesis of 3(2H)-Furanones Initiated by Copper(II)-Catalyzed Alkyne-Carbonyl Cross Metathesis

The cooperative Lewis and Brønsted acid catalysis makes convergent synthesis of 3(2H)-furanones through a three-component coupling of 1,3-diynes, alkyl glyoxylates and water. Control experiments support that Lewis acid-catalyzed highly chemo-, regio- and stereoselective alkyne-carbonyl metathesis of 1,3-diynes and alkyl glyoxylates might be the initial step of this multicomponent annulation. Further chemo- and regioselective hydration of the alkyne-carbonyl metathesis product and subsequent oxa-Michael addition promoted by Brønsted acid results in the formation of two C-O bonds of the five-membered oxygen heterocycle.

Studies towards the Synthesis of (+)-Dictyoxetane

The dolabellane-type diterpene dictyoxetane represents a significant challenge to synthetic organic chemistry. Methodology directed towards the total synthesis of naturally occurring (+)-dictyoxetane is reported. Catalytic asymmetric synthesis of the trans-hydrindane ring system is achieved through chemoselective deoxygenation of the Hajos-Parrish ketone. An alternative to the Garst-Spencer furan annulation is developed for the synthesis of a 2,5-dimethyl, tetrasubstituted furan, employing a tandem 5-exo-dig alcohol to alkyne cyclisation/aromatisation reaction as a key step. The (4+3) cycloaddition reaction of an oxyallyl cation with a tetrasubstituted furan is established on a cyclohexanone-derived model system, and a range of related (4+3) cycloadditions investigated on a homochiral, trans-hydrindane-fused furan, where regio- and diastereoselectivity is required for the natural product synthesis. In an alternative (4+2) Diels-Alder approach, a C2 -symmetric vinyl sulfoxide-based chiral ketene equivalent is used to prepare oxanorbornenes with the same oxygen bridge stereochemistry found in the 2,7-dioxatricyclo[4.2.1.03,8 ]nonane ring system of the natural product.

Asymmetric Total Synthesis of Antibiotic Elansolid A

Elansolid A is a structurally complex polyketide macrolactone natural product that exhibits promising antibacterial properties. Its challenging asymmetric total synthesis was achieved by a convergent strategy, in which the tetrahydroindane core of the molecule and an eastern vinyl iodide moiety were combined as the main fragments. The central tetrahydroindane motif was constructed with high stereoselectivity by a bioinspired intramolecular Diels-Alder cycloaddition, generating four stereogenic centers in a single step. The stereocontrol of this key step could be achieved by virtue of a 1,3-allylic strain generated by the temporary introduction of a steric-directing iodine substituent on the substrate. The formation of the macrolactone motif that completes the synthesis was achieved via two different retrosynthetic disconnections, namely, a Suzuki-Miyaura cross-coupling or an alternative Mukaiyama esterification reaction.

Enantioselective access to tricyclic tetrahydropyran derivatives by a remote hydrogen bonding mediated intramolecular IEDHDA reaction

Inverse-electron-demand-hetero-Diels-Alder reactions of alkenes with α,β-unsaturated keto compounds allow rapid access to the tetrahydropyran ring found in numerous natural products and bioactive molecules. Despite its synthetic interest, catalytic asymmetric versions of this process remain underdeveloped, especially regarding the use of non-activated alkenes reacting with α,β-unsaturated ketone or aldehyde, for which no report can be found in the literature. Herein, we describe the catalytic inverse-electron-demand-hetero-Diels-Alder reactions between neutral alkenes and an α,β-unsaturated ketones or aldehydes to produce a variety of trans-fused [5,6,8] tricyclic structures containing a central, chiral tetrahydropyran ring. This complex transformation, which is achieved using a chiral phosphoric acid, allows for the formation of four stereogenic centers in a single step with high regio-, diastereo- and enantioselectivity (up to 99% ee). Such level of stereocontrol could be achieved by a key remote double hydrogen atom bonding interaction between the linear substrate and the catalyst.

Although the hetero-Diels–Alder reaction is a staple of organic chemistry, catalytic asymmetric versions of the inverse-electron demand variant often require specially engineered substrates for the reaction to work. Here the authors cyclize non-activated alkenes with α,β-unsaturated ketones or aldehydes to form chiral fused heterocycles using a chiral phosphoric acid catalyst.