The unprecedented ring transformation from thiazoline-spiro-thiophene to thieno[2,3-b]pyrazine involved in the reaction of 2-thiocarbamoyl thiazolium salts with dimethyl acetylenedicarboxylate

Reaction of 2-thiocarbamoyl thiazolium salts with dimethyl acetylenedicarboxylate proceeded via a tandem [3+2] cycloaddition and a unprecedented ring transformation to produce functionalized thieno[2,3-b]pyrazine derivatives in good to excellent yields.     

Tandem sigmatropic rearrangements and cyclizations of propargylic dialkoxy disulfides

The first successful preparation of propargylic dialkoxy disulfides in high yields is reported. These esters afforded novel 6,7-dithiabicyclo[3.1.1]heptane-2-one 6-oxide derivatives via an unprecedented sequence of three [2,3]- and one [3,3]-sigmatropic shifts followed by an intramolecular [2+2] cycloaddition. The latter are structurally related to the zwiebelanes, recently isolated from freshly cut onion.     

Novel coordination of dicyanamide, [N(CN)2]-: preferential binding of the amide nitrogen

CoII[N(CN)2]2(H2BiIm)2, 1, and [CoII[N(CN)2](H2BiIm)2]Cl, 2 (H2BiIm = 2,2'-biimidazole) have been structurally, spectroscopically, and magnetically characterized with both containing dicyanamides bound in unprecedented manners; namely, solely via the amide nitrogen for 1, and via an imide N forming 1-D helical chains for 2.     

Copper-Catalyzed Enantioselective Doyle–Kirmse Reaction of Azide-Ynamides via α-Imino Copper Carbenes

[2,3]-Sigmatropic rearrangement reaction involving sulfonium ylide (Doyle–Kirmse reaction) generated from metal carbenes represents one of the powerful methods for the construction of C(sp³)−S and C−C bonds. Although significant advances have been achieved, the asymmetric versions via the generation of sulfonium ylides from metal carbenes have been rarely reported to date, and they have so far been limited to diazo compounds as metal carbene precursors. Here, we describe a copper-catalyzed enantioselective Doyle–Kirmse reaction via azide-ynamide cyclization, leading to the practical and divergent assembly of an array of chiral [1,4]thiazino[3,2-b]indoles bearing a quaternary carbon stereocenter in generally moderate to excellent yields and excellent enantioselectivities. Importantly, this protocol represents a unique catalytic asymmetric Doyle–Kirmse reaction via a non-diazo approach and an unprecedented asymmetric [2,3]-sigmatropic rearrangement via α-imino metal carbenes.     

Organocatalytic synthesis of multiple substituted bicyclo[4.4.0]decalin system

An efficient and unprecedented organocatalytic reaction of γ-nitroketones with α,β-unsaturated aldehydes to give polyfunctionalized [4.4.0] bicyclic skeletons was developed. The diphenylprolinol silyl ether mediated nitro-Michael/Aldol reaction afforded the hexa-substituted decalin carboaldehydes with excellent diastereo- and enantioselectivity (up to >99:1 dr and >99% ee) via a formal [4 + 2] carbocyclization process.     

Asymmetric multicomponent [C+NC+CC] synthesis of highly functionalized pyrrolidines catalyzed by silver(I)

[reaction: see text] Highly functionalized pyrrolidines are obtained in a single chemical step via a mild, efficient, and selective Ag(I)-catalyzed asymmetric [C+NC+CC] coupling process. Oppolzer's camphorsultam enables the desired reaction cascade and provides a reliable means to control the developing stereochemistry and purify the products. This three-component reaction provides unprecedented access to structurally diverse pyrrolidines for both target- and diversity-oriented syntheses.     

A circular tris[2]catenane from molecular 'figure-of-eight'

A 'figure-of-eight'-shaped molecule with Pd(ii) at the node was self-assembled into an unprecedented circular tris[2]catenane via reversible double catenation at both loops of the 'figure-of-eight' molecule.     

Highly Site Selective Formal [5+2] and [4+2] Annulations of Isoxazoles with Heterosubstituted Alkynes by Platinum Catalysis: Rapid Access to Functionalized 1,3‐Oxazepines and 2,5‐Dihydropyridines

Platinum‐catalyzed formal [5+2] and [4+2] annulations of isoxazoles with heterosubstituted alkynes enabled the atom‐economical synthesis of valuable 1,3‐oxazepines and 2,5‐dihydropyridines, respectively. Importantly, this Pt catalysis not only led to unique reactivity dramatically divergent from that observed under Au catalysis, but also proceeded via unprecedented α‐imino platinum carbene intermediates.     

Unexpected syn hydride migration in the non-aldol aldol reaction

[structure: see text] Non-aldol aldol rearrangement of the epoxy silyl ether 13b afforded the expected anti methyl ketone 14, while the diastereomeric epoxy silyl ether 13a afforded the syn methyl ketone 8b via an unprecedented syn hydride migration. Calculations suggest that this unusual reaction proceeds via the carbocation, which cannot easily rotate due to steric hindrance.     

Rhodium(I)-Catalyzed Bridged [5+2] Cycloaddition of cis-Allene-vinylcyclopropanes to Synthesize the Bicyclo[4.3.1]decane Skeleton

Previously reported was that cis-ene-vinylcyclopropanes (cis-ene-VCPs) underwent Rh-catalyzed [5+2] reaction to give 5,7-fused bicyclic products, where vinylcyclopropane (VCP) acts as five-carbon synthon. Unfortunately, this reaction had very limited scope. Replacing the 2π component of cis-ene-VCPs to allene moiety, the corresponding cis-allene-VCPs did not undergo the expected normal [5+2] cycloaddition to give 5,7-fused bicyclic products. Instead, the challenging bicyclo[4.3.1]decane skeleton was obtained via an unprecedented bridged [5+2] cycloaddition. DFT calculations were applied to understand why this bridged [5+2] reaction is favored over the anticipated but not realized normal [5+2] reaction.     

[4 + 3]-Cycloaddition of aza-o-quinone methides and azomethine imines to make 1,2,4-triazepines

In this study, an unprecedented [4 + 3] annulation of aza-ortho-quinone methides with azomethine imines was achieved under mild conditions. Annulation via the aza-Michael/aminalization sequence served as a useful method to synthesize biological heterocycles in good-to-excellent yields.     

Microwave-assisted synthesis of 2,4,5-triaryl-imidazole; a novel thermally induced N-hydroxyimidazole N-O bond cleavage

[reaction: see text] 2,4,5-Triaryl-imidazoles were synthesized directly from the keto-oxime in moderate to good yields via cyclization to the N-hydroxyimidazole and an unprecedented in situ thermal reduction of the N-O bond upon microwave irradiation at 200 degrees C for 20 min.     

Reactivity of functionalized N,S-ketene acetal: regioselective construction of tetrahydrobenzo[b]pyran and chromeno[2,3-b]quinoline derivatives

Regioselective synthesis of functionalized tetrahydrobenzo[b]pyrans has been developed by multicomponent reactions (MCRs) and tandem [3 + 3] annulations of β-benzoylthioacetanilides or β-(2-haloaroyl)thioacetanilides as valuable sources with aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione catalyzed by triethylamine. This MCR followed by a postcondensation cyclization via an intramolecular S(N)Ar in the presence of K(2)CO(3) led to an unprecedented novel chromeno[2,3-b]quinoline framework containing an important chromene moiety in good yields. The reactions were very mild, convenient, and o-selective to form new fused tetracyclic target molecules.     

New strategy for the synthesis of tetrahydroisoquinoline alkaloids

[reaction: see text] A general strategy for the formation of 1,3-cis-substituted tetrahydroisoquinolines is described from ortho-iodo imines involving Larock isoquinoline synthesis, addition of organolithium compounds to unactivated isoquinolines, and ionic hydrogenation. In addition, a new synthesis of lactams via an unprecedented azide cyclization in the presence of a sulfonium ion is described.     

Practical synthesis of a renin inhibitor via a diastereoselective Dieckmann cyclization

A scalable synthesis of a potent renin inhibitor (1) is described. The absolute stereochemistry is set via an unprecedented diastereoselective Dieckmann cyclization directed by a remote chiral protecting group. This transformation enables preparation of chiral 1,3-[3.3.1]-diazabicyclononenes by desymmetrization of alkyl-esters, with selectivities ranging from 4 to 17:1.     

Metal-free synthesis of chromeno[4,3-c]pyrazol-3(2H)-one derivatives

An unprecedented metal-free synthesis of 4-(methylthio)chromeno[4,3-c]pyrazol-3(2H)-one is reported via sequential one-pot desulfitative [5+1] hetero-annulation. The present strategy consists of one-pot sequential, base catalysed dithioketene formation from active methylene of pyrazolone followed by methylation and [5+1] heteroannulative cyclization. The resulting substrate undergoes facile nucleophilic substitution with various amines to yield 4-(substituted-amine)-chromeno[4,3-c]pyrazol-3(2H)-one derivatives under metal free condition.     

Biotransformation of quinovic acid glycosides by microbes: direct conversion of the ursane to the oleanane triterpene skeleton by Nocardia sp. NRRL 5646

[reaction: see text] Quinovic acid glycosides were microbially deglycosylated by a Nocardia sp. to their aglycon quinovic acid and its biogenetic counterpart, cincholic acid (3), via an unprecedented carbon skeleton rearrangement involving a methyl group migration. The structures of the metabolites were established by ESI-LC/MS and 2D-NMR techniques.     

New bicyclotridecane C15 nonterpenoid bromoallenes from Laurencia marilzae

Nonterpenoid bromoallenes possessing a novel skeleton that incorporates an unprecedented [5.5.1]bicyclotridecane ring system, marilzabicycloallenes A-D (1-4), were isolated from specimens of Laurencia marilzae collected on the Canary Islands. The framework of these metabolites strongly reinforces Braddock's hypothesis concerning the biosynthesis via electrophilic bromination of the obtusallene family.     

Li4C60: a polymeric fulleride with a two-dimensional architecture and mixed interfullerene bonding motifs

All known fullerene polymers have interfullerene connections via either [2 + 2] cycloaddition or single C-C bonds. The high-resolution synchrotron X-ray powder diffraction technique was employed here to determine the crystal structure of the Li4C60 fulleride. We find that the ground state of Li4C60 is a two-dimensional polymer with monoclinic crystal symmetry and an unprecedented architecture, combining both the [2 + 2] cycloaddition and the single C-C bridging motifs. The small size of the Li+ cations is crucial in stabilizing the resulting tightly packed polymeric structure.     

Rhodium(I)‐Catalyzed Bridged [5+2] Cycloaddition of cis‐Allene‐vinylcyclopropanes to Synthesize the Bicyclo[4.3.1]decane Skeleton

Previously reported was that cis‐ene‐vinylcyclopropanes (cis‐ene‐VCPs) underwent Rh‐catalyzed [5+2] reaction to give 5,7‐fused bicyclic products, where vinylcyclopropane (VCP) acts as five‐carbon synthon. Unfortunately, this reaction had very limited scope. Replacing the 2π component of cis‐ene‐VCPs to allene moiety, the corresponding cis‐allene‐VCPs did not undergo the expected normal [5+2] cycloaddition to give 5,7‐fused bicyclic products. Instead, the challenging bicyclo[4.3.1]decane skeleton was obtained via an unprecedented bridged [5+2] cycloaddition. DFT calculations were applied to understand why this bridged [5+2] reaction is favored over the anticipated but not realized normal [5+2] reaction.