Total synthesis of (+)-phomopsolide B

An enantiospecific total synthesis of polyhydroxy δ-pyrone natural product phomopsolide B is accomplished. The main feature of the synthesis is the installation of the required E-olefin by Horner–Emmons–Wordsworth reaction and the formation of the lactone involving Still–Gennari olefination followed by lactonization.     

Total synthesis of (+)-hatomarubigin B.

The first total synthesis of (+)-hatomarubigin 3 is described. The tetra-O-acetyl diborate promoted Diels-Alder reaction of 5-hydroxy-8-(2',3',4',6'-tetra-O-acetyl-beta-D-glucopyranosyloxy)-1,4-naphthoquinone 8 and (E, 1R*,5R*)-3-(2'-methoxyvinyl)cyclohex-2-enol (+/-)-7 gave a mixture of four cycloadducts from which (1S,3S,6S,6aR,12aR,12bS)-1,8-dihydroxy-6-dimethoxy-1-hydroxy-3-methyl-11-(2',3',4',6'-tetra-O-acetyl-beta-D-glucopyranosyloxy)-1,2,3,4,6,6a,12a,12b-octahydrobenz[a]anthracene-7,12-dione 12 was isolated in 51% yield. Selective methylation and acetylation of 12 gave (1S,3S,6S,6aR,12aR,12bS)-1-acetoxy-6,8-dimethoxy-3-methyl-11-(2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyloxy)-1,2,3,4,6,6a,12a,12b-octahydrobenz[a]anthracene-7,12-dione 10a. Sequential aromatization, photooxidation and hydrolysis of the glucosyl unit gave (+)-3 (98% ee) in an 8% overall yield from 8.     

Total synthesis of (+)-allocyathin B2

The first enantioselective synthesis of (+)-allocyathin was achieved. The synthesis features a Pd-catalyzed asymmetric allylic alkylation to install the first quaternary center, a Ru-catalyzed diastereoselective cycloisomerization to construct the six-membered ring, and a diastereoselective hydroxylative Knoevenagel reaction to introduce the final hydroxyl group. The unusual olefin isomerization of the Ru-catalyzed cycloisomerization was discussed and exploited for the synthesis.     

Total synthesis of (+)-anamarine

Total synthesis of (+)-anamarine a polyoxygenated δ-pyranone natural product was accomplished via cross-metathesis protocol starting from 3-butene-1-ol and glycidol. Other key features of this synthetic strategy include use of Sharpless asymmetric epoxidation, dihydroxylation, and deoxygenation-isomerization through allene rearrangement.     

Total synthesis of (+)-strictifolione

[reaction: see text] The synthesis of (+)-strictifolione was achieved from 3-phenylproprionaldehyde by using enantioselective allyltitanations to control the stereogenic centers at C6, C4', and C6' and a cross-methathesis to control the configuration of the double bond at C1'-C2'.     

Total synthesis of (+)-laurallene

The stereoselective total synthesis of (+)-laurallene is described. The required key oxocene skeleton possessing trans-orientated alkyl substituents at the α,α′-positions was stereoselectively constructed via the cyclization of the corresponding hydroxy epoxide promoted by Eu(fod)₃.     

Total synthesis of (+)-conagenin

The total synthesis of the immunomodulator, (+)-conagenin was achieved using, as a key step, a method developed by us for the synthesis of 2-methyl-1,3-diols via Ti(III)-mediated diastereo- and regioselective opening of trisubstituted 2,3-epoxy alcohols, to carry out the stereoselective construction of its pentanoic acid segment.     

Total synthesis of (+)-dactylolide

[reaction: see text] The development of an approach leading to the total synthesis of dactylolide is described. The key features of this route include a catalytic asymmetric allylation, a diastereoselective pyran annulation, and a Horner-Wadsworth-Emmons macrocyclization.     

Total synthesis of (+)-astrophylline

The first total synthesis of (+)-astrophylline (2) has been achieved, starting from readily available enantiomerically pure (+)-(1R,4S)-4-hydroxycyclopent-2-enyl acetate (11). A novel ruthenium-catalyzed ring-closing ring-opening ring-closing metathesis of carbocyclic olefins of general type 5 was the key step, providing the stereochemically well-defined bis-piperidyl skeleton of the target molecule. A [2,3]-Wittig-Still rearrangement of 9 was also employed as the critical transformation in the stereocontrolled generation of the 1,2-trans configuration of the cyclopentene intermediate 6c. Our early synthetic efforts toward 1,2-trans cyclopentene derivatives of type 6, as well as the synthetic pathway to an optimized 13-step total synthesis of 2 (12% overall yield), are reported.     

Total synthesis of (+)-asteltoxin

A convergent synthesis of (+)-asteltoxin (1) has been achieved by the Horner-Emmons olefination of bis(tetrahydrofuran) aldehyde 53 and alpha-pyrone phosphonate 5. A key step features the stereoselective construction of a sterically congested quaternary center embedded in the densely functionalized bis(tetrahydrofuran) subunit by a Lewis acid-catalyzed, pinacol-type rearrangement of an epoxy silyl ether. This pivotal rearrangement methodology parallels the proposed biosynthetic pathway of 1 and is ripe for applications to the stereocontrolled synthesis of structurally complex natural products.     

Total synthesis of (+)-anamarine

An enantiospecific total synthesis of polyhydroxy δ-pyrone natural product (+)-anamarine is accomplished. The main features of the synthesis include the stereoselective reduction of the ketone obtained by the desymmetrization of the bis-dimethyl amide of tartaric acid and further elaboration involving asymmetric Brown's allylation and ring closing metathesis.     

Total synthesis of (+)-pseudohygroline

A simple and efficient total synthesis of five-membered pyrrolidine, (+)-pseudohygroline is described. The key steps involved in this synthesis are highly stereoselective Prins cyclisation followed by reductive ring opening and hydroboration.     

Total synthesis of (+)-obtusenyne

The stereoselective total synthesis of (+)-obtusenyne is described. The oxonene skeleton possessing trans-orientated alkyl substituents at the α,α′-positions was stereoselectively constructed via cyclization of the corresponding hydroxy epoxide promoted by Eu(fod)₃.     

Total synthesis of (+)-kalkitoxin

The neurotoxic lipopeptide (+)-kalkitoxin was synthesized by a route which employed asymmetric organocopper conjugate addition followed by in situ enolate alkylation to install the anti,anti-1,2,4-trimethyl relationship of the toxin; the synthesis of kalkitoxin required sixteen steps and proceeded in 3% overall yield.