Stereoselective synthesis of (±)-erythro- and threo-γ-hydroxynorvaline

Both diastereomers of racemic γ-hydroxynorvaline were prepared from 4-penten-2-ol to illustrate a new general method for stereoselective synthesis of either erythro- or threo-1,3-amino alcohol systems from a single precursor.     

Stereoselective total synthesis of (±)-peribysin E

Radical cyclization of iodoketone 3 afforded cis-hydrindanone 8. Compound 8 was converted into key intermediate 5 via conventional transformations. Annulation of a spiro-lactal unit to 5 was pursued with three different approaches. In the first approach, radical cyclization of propargyl ester 17 provided spiro-lactone 18 with an undesired stereochemistry. Attempts to invert the stereochemistry at the spiro-center via retro-aldol and aldol condensation of compound 20 failed. In the second approach, key intermediate 5 was transformed into 23. Acylation of compound 23 gave 24 as a single diastereomer with the desired stereochemistry but in low yield. NBS bromination of 24 followed by lactone formation gave 26 in low yield. Alternatively, allylic oxidation of 24 with SeO(2) followed by lactonization gave 26 also in low yield. Finally, a third approach employing a semipinacol-type rearrangement of epoxy-alcohol 33 gave aldehyde 34 with the desired stereochemistry. Treatment of compound 34 with HCl in MeOH effected spiro-lactal formation and provided (±)-peribysin E. The overall yield of our synthesis is 3.2% from 2-methylcyclohenen-1-one.     

Total synthesis of (±)-maistemonine and (±)-stemonamide

The first total synthesis of polycyclic Stemona alkaloid maistemonine has been achieved. The efficient approach features a stereoselective intramolecular Schmidt reaction, a ketone-ester condensation, and a Reformatsky reaction. Additionally, another Stemona alkaloid stemonamide was divergently synthesized from a common intermediate.     

Stereoselective synthesis of (±)-threo-γ-hydroxy-β-lysine lactone

A stereoselective synthesis of racemic threo-γ-hydroxy-β-lysine is reported. The threo aminoalcohol functionality is introduced by mercuric-ion initiated cyclofunctionalization of the acylaminomethyl ether 4a.     

Stereoselective Synthesis of (±) Neocnidilide

The lactone neocnidilide 8 occur in the roots of Cnidilide officinale1 which is shown to inhibit the growth and toxin production of mycotoxin-producing fungi2. Although The synthesis of lactones 7, which is stereoisomer of cnidilide, and 8 had been reported by others3, 4, we would like to report the highly stereoselective synthesis of its racemic isomer 8 as shown in Scheme 1. Scheme 1 COOHHOOCbcOOHH1234d5eOHOHHH 6fOOHHH 7g8COOHOHa12345673a7aOHHOH1235673 a7a1234561'1'2'…     

Stereoselective synthesis of (±)-tetraponerine-8, a defence alkaloid of the ant Tetraponera sp.

The title compound has been stereoselectively synthesized in 6 steps.     

Total synthesis of (±)-cycloclavine and (±)-5-epi-cycloclavine

Novel routes to the naturally occurring indole alkaloid cycloclavine and its unnatural C(5)-epimer are described. Key features include the rapid construction of the heterocyclic core segments by two Diels-Alder reactions. An indole annulation was accomplished by a late-stage intramolecular Diels-Alder furan cycloaddition, and a methylenecyclopropane dienophile was used for a stereoselective intramolecular [4 + 2] cycloaddition to give the cyclopropa[c]indoline building block present in cycloclavine.     

Total synthesis of (±)-maistemonine, (±)-stemonamide, and (±)-isomaistemonine

A full account of the total synthesis of (±)-maistemonine, (±)-stemonamide, and (±)-isomaistemonine is presented. Two approaches have been developed to construct the basic pyrrolo[1,2-a]azepine core of the Stemona alkaloids, featuring a tandem semipinacol/Schmidt rearrangement of a secondary azide and a highly stereoselectively desymmetrizing intramolecular Schmidt reaction, respectively. To build the common spiro-γ-butyrolactone, a new protocol was carried out by utilizing an intramolecular ketone-ester condensation as the key transformation. The vicinal butyrolactone moiety of (±)-maistemonine was stereoselectively introduced via a one-pot procedure involving the epimerization at C-3 and carbonyl allylation/lactonization. Moreover, (±)-stemonamide was divergently synthesized from a common intermediate, and (±)-isomaistemonine was obtained via the epimerization of (±)-maistemonine at C-12.     

Stereoselective total synthesis of (±)-isolobophytolide,a marine cembranolide natural product

The total synthesis of (±)-isolobophytolide (20) has been achieved via a route involving piallyl palladium initiated macrocyclization of sulfone ester 8 and subsequent carboxy inversion of the macrocyclic acid 11 to introduce the C-14 lactone oxygen. Lactone α-methylenation was effected by dehydration of the hydroxymethyl derivative 19 with 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide metho-p-toluenesulfonate-CuCl₂.     

First total synthesis of (±)-puyanin and (±)-4'-O-methylbonannione

<正>A facile approach for the first total synthesis of two naturally occurring geranylated flavonoids,(±)-puyanin 1 and(±)-4'-O- methylbonannione 2 has been obtained with total yield 27%and 21%,respectively.The key steps were regioselective cyclization of geranylated trihydroxychalcone and regioselective geranylation of 2,4,6-trihydroxyacetophenone.     

Total synthesis of (±)-hibiscone B and (±)-acyl hibiscone B

The first total syntheses of the furanosesquiterpenoids hibiscone B and acyl hibiscone B are reported. The chemistry used to prepare hibiscone B solves an important challenge to the synthesis of other members of the furanosesquiterpenoid family of natural products, for which the parent molecule, hibiscone C, has shown promising biological activity.     

Total synthesis of (±)-pallambins C and D

The first total synthesis of (±)-pallambins C and D has been accomplished in a linear 38 step reaction from (±)-Wieland-Miescher ketone. The key conversions are featured as follows: a Grob fragmentation-intramolecular aldol cyclization and a thiourea/palladium-catalyzed carbonylative annulation.     

Fast and protecting-group-free synthesis of (±)-subincanadine C

The first total synthesis of (±)-subincanadine C has been accomplished in a protecting-group-free fashion. This pentacyclic indole alkaloid was synthesized in six steps from the known intermediate 4, featuring Ni(COD)(2)-mediated intramolecular Michael addition as a key transformation.     

The synthesis of (±)-cavernosine

The title compound and its epimer were synthesized in three and two steps from dihydro-β-ionone and 2-trimethylsiloxyfuran in 38 and 63% overall yields respectively. Their relative configurations were confirmed by X-ray of an intermediate.     

Total synthesis of (±)-cephalosol

A concise and efficient total synthesis of (±)-cephalosol has been completed (5 steps from known ester 5, 39% overall yield), featuring a Cu(II)-promoted haloisocoumarin formation and sequential Suzuki cross-coupling/intramolecular oxo-Michael addition.