Total synthesis of (+)-balanitol and of (+)-selin-4-(15)-ene-1β,11-diol

(+)-Balanitol (1) and (+)-selin-4-(15)-ene-1β,11-dio1 (2), two recently-isolated naturally occurring eudesmanoid bicyclic sesquiterpene alcohols, have been synthesized stereoselectively by a route involving a [2 +2] photocycloaddition of a cyclobutene and a suitably structured 2-cyclohexenone. The structure and stereochemistry of the compounds are thereby corroborated.     

Diastereoselective synthesis of syn-aminoalcohols via contributing CH-π interaction: simple synthesis of (−)-bestatin

¹H NMR and X-ray crystallography studies revealed that a CH-π and chelation control in aromatic aminoaldehydes (1-6) effects a highly diastereoselective addition to afford optically active syn-aminoalcohols (1a-6a). This methodology was applied to the synthesis of (−)-bestatin.     

Synthesis of (+)-altholactone, (+)-7-epi-altholactone, (−)-etharvensin,and (+)-alumheptolide-A using Pd-catalyzed carbonylation

Syntheses of (+)-altholactone isolated from Goniothalamus giganteus and its C-7 epimer (+)-7-epi-altholactone, (?)-etharvensin and (+)-alumheptolide-A were achieved. The lactone ring of these compounds was constructed using Pd-catalyzed carbonylation.     

Enantiodivergent synthesis of (+)- and (−)-isolaurepan

The enantiodivergent synthesis of (+)-and (?)-isolaurepan was achieved from a common chiral template easily available from tri-O-acetyl-d-glucal, using as key step a diastereoselective thermal Claisen rearrangement, combined with a ring expansion reaction using trimethylsilyldiazomethane.     

Facile synthesis of (−)-tabtoxinine-β-lactam and its (3′R)-isomer

A concise and high yielding synthesis of (−)-tabtoxinine-β-lactam 1, the cause of tobacco wildfire disease, was achieved from l-serine using a zinc-mediated coupling reaction, Sharpless asymmetric dihydroxylation and lactamization of N-OBn amide as the key steps.     

RCM/PCC oxidation strategy for synthesis of functionalized cyclic α,β-unsaturated lactones: synthesis of (+)-triacetoxygoniotriol and its diastereomers

A novel methodology leading to the synthesis of (+)-triacetoxygoniotriol 2 from d-glucose is described. Construction of the core six-membered α,β-unsaturated lactone moiety involved ring closing metathesis (RCM) followed by a PCC oxidation. Later exploiting the pseudo-symmetry of d-glucose three other diastereomers of triacetoxygoniotriol were synthesized using the developed methodology.     

Asymmetric synthesis of (+)-preussin from N-sulfinyl δ-amino β-ketoesters

The efficient asymmetric synthesis of the antifungal pyrrolidine alkaloid (+)-preussin (2) was accomplished via the stereoselective reduction of a 5-substituted 3-oxo proline. The oxo proline was prepared from an N-sulfinyl δ-amino β-ketoester, a sulfinimine derived polyfunctionalized chiral building block.     

Stereocontrolled synthesis of substituted chiral piperidines via one-pot asymmetric 6π-azaelectrocyclization: asymmetric syntheses of (-)-dendroprimine, (+)-7-epidendroprimine, (+)-5-epidendroprimine, and (+)-5,7-epidendroprimine

The asymmetric one-pot 6π-azaelectrocyclization of alkenyl vinyl stannane, ethyl (Z)-2-iodo-4-oxobutenoate, and (-)-7-isopropyl-cis-aminoindanol in the presence of a Pd(0) catalyst stereoselectively produced the tetracyclic aminoacetal compounds, resulting from the four-bond formation accompanying by controlling the stereochemistry at the two asymmetric centers. The produced cyclic aminoacetals can be regarded as synthetic precursors of substituted chiral piperidines, and the syntheses of 2,4- and 2,4,6-substituted piperidines were realized from the obtained aminoacetals by the stereoselective hydrogenation of the double bond conjugated with the C-4 ester group and alkylation at the aminoacetal moiety. In addition, the stereoselective synthesis of an indolizidine alkaloid, (-)-dendroprimine, and its three stereoisomers, (+)-7-epidendroprimine, (+)-5-epidendroprimine, and (+)-5,7-epidendroprimine, were achieved.     

The first stereoselective total synthesis of (3S,4R)-dihydroxy-(6S)-undecyl-α-pyranone and total synthesis of (2S,3R,5S)-(−)-2,3-dihydroxytetradecan-5-olide

The first total synthesis of (3S,4R)-dihydroxy-(6S)-undecyl-α-pyranone 1 and total synthesis of (2S,3R,5S)-(−)-2,3-dihydroxytetradecan-5-olide 2 have been achieved in five steps in a highly stereoselective manner using Maruoka allylation, olefin cross-metathesis, and Sharpless asymmetric dihydroxylation as key steps.     

An expedient total synthesis of optically active piperidine and indolizidine alkaloids (−)-β-conhydrine and (−)-lentiginosine

Attempts directed toward the stereocontroled total synthesis of piperidine and indolizidine alkaloids resulted in the synthesis of (−)-β-conhydrine 1 and (−)-lentiginosine 3. The synthesis of 1 and 3 were developed from protected d-mannitol as the chiral precursor, which involved nucleophilic addition and azide nucleophilic substitution, Barbier allylation, ring closing metathesis, and Sharpless asymmetric dihydroxylation as the key steps.     

A novel stereoselective synthesis of (−)-β-conhydrine from (R)-2,3-O-cyclohexylidine glyceraldehyde

A novel stereoselective synthesis of (−)-β-conhydrine is achieved. Stereoselective Grignard reaction of (R)-2,3-O-cyclohexylidine glyceraldehyde with ethyl magnesium bromide, chelation controlled stereoselective Grignard reaction of allyl imine derivative with allyl magnesium bromide, and ring-closing metathesis (RCM) of the diallyl product provides (−)-β-conhydrine in high yield.     

The synthesis, crystal chemistry and structures of Y-doped brannerite (U1−xYxTi2O6) and thorutite (Th1−xYxTi2O6−δ) phases

Yttrium-doped uranium brannerite (U_1−xY_xTi₂O₆) and thorutite (Th_1−xY_xTi₂O_6−δ) phases were synthesized in air at 1400°C. Powder X-ray diffraction revealed that these phases crystallized to form monoclinic (C2/m) structures. Crystal structures of U_0.54Y_0.46Ti₂O₆ (1) (a=9.8008(2); b=3.7276(1); c=6.8745(1); β=118.38(1); V=220.97(1); Z=2; R_P=7.3%; R_B=4.6%) and Th_0.91Y_0.09Ti₂O_6−δ (2) (a=9.8002(7); b=3.7510(3); c=6.9990(5); β=118.37(4); V=226.40(3); Z=2; R_P=4.5%; R_B=2.9%) were refined from powder neutron diffraction data. These two phases were isostructural, revealing planes of corner and edge-sharing TiO₆ octahedra separated by irregular eight-fold coordinate U/Y or Th/Y atoms. The oxygen sites within the structure of 1 were found to be fully occupied, confirming that the doping of lower valence Y atoms occurs in conjunction with the oxidation of U(IV) to U(V). Y doping of the thorutite phase 2 does not lead to oxidation but rather the formation of oxygen vacancies within the structure.     

A stereoselective total synthesis of (+)-α-herbertenol

A stereoselective total synthesis of (+)-α-herbertenol starting from the allyl alcohol 12, readily available in three steps from the monoterpene (R)-limonene, is described. Claisen rearrangement of the aryl allyl ether 10 and concomitant cyclisation furnished a 5:3 mixture of the tricyclic compounds 13 and 14. Degradation of the isopropenyl group followed by cleavage of the central ring and functional group manipulation transformed 13 into (+)-α-herbertenol (1b).     

A new and convenient synthesis of protoberberine alkaloids: (±)-tetrahydropalmatine, (±)-sinactine, (±)-canadine,and (+)-stylopine

2,3,9,10-Tetraoxygenated protoberberine alkaloids (14) were efficiently synthesized from the readily available benzaldehyde (2 or 10) via the benzylphenethylamines (11) and 2-phenethylisoquinolin-3-ones (12 and 13).     

Asymmetric synthesis and biosynthetic implications of (+)-fusarisetin A

Starting from equisetin, the asymmetric synthesis of (+)-fusarisetin?A has been accomplished in a one-pot transformation including a biomimetic oxidation and an intramolecular Diels-Alder/Roskamp reaction. Peroxyfusarisetin is proposed as a plausible biosynthetic intermediate based on studies of the oxidation of equisetin.     

Novel rare-earth borosilicide RE1−xB12Si3.3−δ (RE=Y, Gd-Lu) (0?x?0.5, δ≈0.3): synthesis, crystal growth, structure analysis and properties

New rare-earth boron-rich compounds with the formula of RE_1−xB₁₂Si_3.3−δ (RE=Y, Gd-Lu) (0?x?0.5,δ≈0.3) have been synthesized. They belong to a new type of rhombohedral structure with the space group of R-3m (No. 166) and z=9. The lattice constants were measured from powder XRD data. Crystal structure solved from powder XRD data for Tb_0.68B₁₂Si₃ as a representative has been compared with that of YB_17.6Si_4.6 (or Y_0.68B₁₂Si_3.01), whose structure was solved from single-crystal reflection data. The structure model is confirmed by high-resolution transmission microscope analysis. The vibrational modes of the new crystals were measured by Raman spectroscopy. Temperature dependence of magnetic susceptibility which was measured for RE_1−xB₁₂Si_3.3−δ single crystals by SQUID revealed that they are paramagnetic materials down to 2.0 K.     

( S )-(?)-α-Methylbenzylamine as chiral auxiliary in the synthesis of (+)-lortalamine

Abstract  

(+)-Lortalamine was synthesised using (S)-(−)-α-methylbenzylamine as a chiral auxiliary. The stereochemistry of an intermediate compound was established on the basis of X-ray crystallography, allowing unambiguous assignment of the absolute configuration.     

Studies on the synthesis of chiral nonracemic 3,4-disubstituted azepanes,a formal synthesis of (+)- and (−)-balanol

Sugar lactones were converted to 3,4-disubstituted azepanes and caprolactam derivatives by selective deoxygenation, functionalization and reductive cyclization. The cyclization proved troublesome with 6-azidolactols but led to good results with the corresponding lactones. A formal synthesis of (+)- and (−)-balanol is reported.     

Efficient synthesis of (−)-(R)- and (+)-(S)-rolipram

A novel, efficient and protecting group free enantioselective synthetic approach of (?)-(R)-1 and (+)-(S)-rolipram 2 is described employing the organocatalyzed asymmetric Michael addition, Henry condensation, Wittig olefination and reductive lactamization reactions as key steps.