cis-Selective, Enantiospecific Addition of Donor-Acceptor Cyclopropanes to Activated Alkenes: An Iodination/Michael-Cyclization Cascade

We present a versatile method for the enantiospecific, cis-diastereoselective intermolecular and intramolecular cycloaddition of donor-acceptor cyclopropanes to electron-poor alkenes with cyclic acceptor groups to afford highly substituted spirocyclopentanes in good to excellent yields. The reaction can be applied to biologically interesting scaffolds, including barbiturates and isoxazolones. Mechanistic investigations were undertaken to explain the unusual diastereoselectivity and enantiospecificity; these suggest an iodination/Michael-cyclization cascade.

Donor-Acceptor Cyclopropanes in the Synthesis of Carbocycles

Donor-acceptor cyclopropanes not only participate in a broad range of ring openings with nucleophiles, electrophiles, radical and red-ox agents, but also are excellent substrates for various (3+n)-cycloaddition and (3+n)-annulation processes. Moreover, under treatment with Lewis acid donor-acceptor cyclopropanes can produce new ring systems via isomerization or cyclodimerization. Authors' contribution to the synthesis of diverse carbocycles from donor-acceptor cyclopropanes is summarized in this account.

Stereoselective Synthesis of Fused Vinylcyclopropanes by Intramolecular Tsuji-Trost Cascade Cyclization

A stereoselective intramolecular Tsuji–Trost cascade cyclization of (homo)allylic vicinal diacetates with a pendant β-ketoamide or related carbon nucleophile to give γ-lactam-fused vinylcyclopropanes is reported. In addition to two new rings, the products contain three new C–C stereocenters (two of which are quaternary) with a 9:1 dr. Moreover, the reaction proceeds in >94% enantiospecificity with optically enriched starting materials, using an inexpensive carbohydrate as the source of chirality.

Cytotoxic monoterpenoid-type alkaloids from the aerial parts of Melodinus morsei

Three new monoterpenoid alkaloids, melomorines A-C (1-3), along with melohemsine B (4), were isolated from the 70% ethanol extract of the aerial parts of Melodinus morsei. Structural elucidation of all the compounds was performed on the basis of spectral data. All the compounds were tested in vitro for cytotoxic activities. As a result, alkaloids 1, 2, and 4 exhibited cytotoxicities against all the five tested tumor cell lines with IC₅₀ value of less than 20 μM.

Lewis Acid Triggered Vinylcyclopropane-Cyclopentene Rearrangement

We report a mild Lewis acid induced isomerization of donor-acceptor cyclopropanes, containing an alkenyl moiety and diverse electron-withdrawing group(s) at the adjacent positions, into substituted cyclopentenes. We have found that 1,1,2-trisubstituted cyclopent-3-enes were exclusively obtained in yield of 51-99% when cyclopropanes with a 2-substituted alkenyl group as a donor underwent isomerization. For cyclopropanes bearing a trisubstituted alkenyl group either the corresponding cyclopent-3-enes or isomeric cyclopent-2-enes having two acceptor groups at the C(1) atom were formed, with the reaction selectivity being determined by the applied Lewis acid. We have shown that the reactivity of the donor-acceptor cyclopropane increases with the increase of the electron-donating character of (hetero)aromatic group attached to the alkenyl moiety. The synthetic utility of the developed methodology was also demonstrated through the synthesis of polysubstituted cyclopentane and piperidine derivatives.

Harnessing sunlight without a photosensitizer for highly efficient consecutive [3+2]/[4+2] annulation to synthesize fused benzobicyclic skeletons

A photosensitizer-free, highly efficient sunlight-promoted tandem [3+2]/[4+2] annulation of unsaturated α-bromocarbonyls with o-alkynylanilines was described, and allowed for convenient synthesis of fused benzobicyclic skeletons.

Diastereoselective Intramolecular [3 + 2]-Annulation of Donor-Acceptor Cyclopropane with Imine-Assembling Hexahydropyrrolo[3,2-c]quinolinone Scaffolds

An intramolecular [3 + 2]-annulation of amide-linked donor-acceptor cyclopropane with in situ-generated imine is described. As a result, diverse hexahydropyrrolo[3,2-c]quinolinones, as the tricyclic core of martinellines, were efficiently assembled in good to excellent yield (up to 93%) with a good diastereomeric ratio (up to 98:2).

Melohemsines A-I, melodinus-type alkaloids from Melodinus hemsleyanus

Melohemsines A-I (1–9) were obtained from Melodinus hemsleyanus. 1 is the first melodinus-type alkaloid possessing a 6/6/5/5/6/3 six ring skeleton system. 2 and 3 are the first natural melodinus-type alkaloids with a reduction of two carbon units at C-20.