A new convergent route to aldohexoses from a common chiral building block

[reaction in text] A diastereocontrolled route to the eight aldohexoses has been developed starting from a common cyclohexanoid chiral building block.     

A new route to (+)-estrone using a bicyclo[3.2.1]octane chiral building block

A new route to (+)-estrone has been developed starting from the chiral building block having a bicyclo[3.2.1]octane framework based on the inherent stereochemical chemical nature of the chiral building block.     

A new route to diverse 1-azasugars from N-Boc-5-hydroxy-3-piperidene as a common building block

A new general method for the synthesis of a variety of 1-azasugars with a nitrogen atom at the anomeric position is described. The readily available chiral N-Boc-5-hydroxy-3-piperidene 3 is transformed to isofagomine (2), homoisofagomine (13), and 5'-deoxyisofagomine (14) via stereoselective epoxidation and regioselective ring-cleavage in a highly stereocontrolled manner. In addition, the synthesis of all four stereoisomers of 3,4,5-trihydroxypiperidines (18-21) classified as 1-azasugar-type glycosidase inhibitors was stereoselectively achieved from the (chiral) piperidene 3.     

A concise synthetic route to the conduritols from pentoses

A short synthetic strategy for preparation of the conduritols is described. The key step employs a zinc-mediated fragmentation of protected methyl 5-deoxy-5-iodo-d-pentofuranosides followed by an allylation of the intermediate aldehyde in the same pot. The allylation is performed with 3-bromopropenyl benzoate and occurs with good diastereoselectivity. An amino group can be introduced in the product by trapping the intermediate aldehyde as the imine prior to the allylation. The functionalised 1,7-octadienes, thus obtained, are converted into protected conduritols by ring-closing olefin metathesis.     

A general and stereoselective route to alpha- or beta-galactosphingolipids via a common four-carbon building block

A general synthetic strategy toward alpha- or beta-galactosylceramides and their analogues from 3-azido-2-O-benzyl-1-O-(4-methoxybenzyl)butane-1,2,4-triol is described. The key steps for the installation of the main lipid chain are either a diasteroselective alkynylation reaction yielding the 4R stereocenter of phytosphingosine or a Wittig olefination generating the trans double bond of sphingosine. The methodology allows the preparation of different glycolipids with variations in the structure of the sphingoid base. In particular, three alpha-GalCer-related compounds have been synthesized and evaluated for their ability to activate CD1d-restricted T-cells.     

Asymmetric synthesis of 1-deoxynojirimycin and its congeners from a common chiral building block

A new, promising chiral building block 9 for the synthesis of 1-deoxy-4,5-trans-oriented azasugars such as 1-deoxynojirimycin (1) was prepared in only four steps from the Garner aldehyde 10 using catalytic ring-closing metathesis (RCM) for the construction of the piperidine ring. In practical test, the first synthesis of all four isomers (1 and 6-8) of trans-4,5-orientated 1-deoxyiminosugars using 9 as a common chiral building block was demonstrated.     

Asymmetric synthesis of (+)-isofebrifugine and (-)-sedacryptine from a common chiral nonracemic building block

The stereoselective syntheses of 2-substituted and 2,6-disubstituted 3-hydroxypiperidine alkaloids, (+)-isofebrifugine and (-)-sedacryptine, from a common, functionalized nonracemic bicyclic building block are achieved, demonstrating the flexibilty of the approach.     

A facile convergent route to dendritic polyols

The synthesis of monodisperse dendrimers triggers a great challenge to the synthetic chemistry. Here, we reported a facile convergent approach to the synthesis of the first generation, six-directional ether-bond polyols with better controlled structures and ease of purification.     

Indoles from 3-nitropyridinium salts: A new route to chiral indoles and indolines

(S)-1-(1-Methylbenzyl)-2,4,6-trimethylindole was prepared by interaction of (S)-isopropyliden(1-methylbenzyl)amine with 1,2,4,6-tetramethyl-3-nitropyridinium iodide. The indoles thus prepared undergo diastereoselective hydride reduction and debenzylation to afford chiral (S)-2,4,6-trimethylindoline with high yield and optical purity up to 76%.     

Asymmetric reduction of azirines; a new route to chiral aziridines

The first enantioselective reduction of aromatic 2H-azirines yields aziridines in up to 70% ee, using the aminoalcohol-[RuCl2(p-cymene)]2 catalyzed asymmetric transfer hydrogenation reaction.     

Facile convergent route to indoloquinolines

A convergent route to indoloquinolines is developed through aldol condensation. This two-step method utilizes commercially available 2-oxoindole and o-nitrobenzaldehyde as starting materials. Chromatography-free method is accomplished for preparing several derivatives of indoloquinolines with desirable aromatic substitutions on indole as well as quinoline ring.     

A concise synthesis of (+)-pancratistatin using pinitol as a chiral building block

A concise approach toward (+)-Pancratistatin has been achieved via 12 steps from pinitol. An ultrasound assisted arylcerium induced ring opening of cyclic sulfate was employed as a key step.     

Sequential Birch reaction and asymmetric Ir-catalyzed hydrogenation as a route to chiral building blocks

A range of 1,2,4-trisubstituted cyclohexadienes obtained from the Birch reaction were hydrogenated asymmetrically to produce synthetically valuable chiral compounds in high enantio- and diastereoselectivity.     

A new synthetic route to chiral 3-aryl-5-ethyl-1,4,2-oxazaphosphorines

1. Download high-res image (94KB)
2. Download full-size image

     

A convergent rgiospecific route to the aklavinone ring system

A convergent regiospecific route to the aklavinone (II) ring system is described.     

A simple route to chiral phosphinous acid-boranes

We report a simple one-pot synthesis of enantiomerically enriched alkyl- and arylphenylphosphinous acid-borane starting from readily available (R(P))-(-)-menthylhydrogenophenylphosphinate and organolithium reagents.     

A convergent route to the CDEF-tetracycle of pectenotoxin-2

A convergent synthesis of the CDEF-tetracyclic region of pectenotoxin-2 (PTX-2) is described. The synthetic pathway derives from a head-to-tail union of 2 equiv of linalool to establish a stereodefined DEF-tricyclic aldehyde. Subsequent coupling with a "northern" fragment enolate, followed by a tandem Sharpless epoxidation/cyclization, delivers the C10-C26 polycyclic region of the natural product.     

A "chiral aldehyde" equivalent as a building block towards biologically active targets

Chiral gamma-aryloxybutenolides, readily accessible through dynamic kinetic asymmetric transformation (DYKAT) of racemic acyloxybutenolides, were utilized as "chiral aldehyde" building blocks for intermolecular cycloadditions and Michael reactions. Unprecedented selectivity in trimethylenemethane cycloadditions with this building block allowed an efficient synthesis of a novel metabotropic glutamate receptor 1 antagonist in development by the Bayer corporation. These studies further inspired work that culminated in the total synthesis of (+)-brefeldin A, a natural product with a range of significant biological properties. All of the stereochemistry in this target molecule was derived from two palladium-catalyzed asymmetric allylic alkylation reactions. The trans-alkenes were synthesized by a Julia olefination and a ruthenium-catalyzed trans-hydrosilylation-protodesilylation protocol. The route to (+)-brefeldin A lends itself to analogue syntheses and was completed in 18 steps in 6 % overall yield.     

A cascade cyclization route to adjacent bistetrahydrofurans from chiral triepoxyfarnesyl bromides

A number of isomeric bistetrahydrofuran analogues were prepared from triepoxy farnesyl bromides by a zinc-initiated reduction-elimination and in situ Lewis acid-promoted cascade cyclization.