Recent advances in the total synthesis of polyhydroxylated alkaloids via chiral oxazines.

This review summarizes recently established methodologies developed for the enantioselective and diastereoselective synthesis of chiral 1,3-oxazines. These compounds are of interest as advanced synthetic intermediates in the total synthesis of structurally complex and biologically active polyhydroxylated alkaloids such as (+)-1-deoxynojirimycin, (-)-anisomycin, (+)-castanospermine, (+)-casuarine, (-)-conduramine F-1, (-)-sphingofungin B, Neu5Ac methyl ester, and other natural products. The devised synthetic approach aims to offer a direct, efficient, and adaptable method for obtaining both pure enantiomers and pure diastereomers. It revolves around utilizing chiral building blocks like syn,syn-, syn,syn,anti-, syn,anti-, syn,anti,syn-, anti,syn-, anti,syn,syn-, and anti,syn,anti-oxazines. By integrating oxazine chemistry with established and innovative transformations, this approach enabled the synthesis of 30 polyhydroxylated amines across various studies conducted between 2007 and 2022.

Stereoselective Total Syntheses of (+)-Castanospermine and Neu5Ac Methyl Ester.

Concise and stereocontrolled total syntheses of (+)-castanospermine and N-acetylneuraminic acid methyl ester were achieved from diastereomerically enriched anti, syn, syn-1,3-oxazine and anti, syn, anti-1,3-oxazine, respectively. The key step in this strategy was the stereoselective BF3·OEt2-mediated allylation.

Stereoselective Chirality Extension of syn,anti- and syn,syn-Oxazine and Stereochemical Analysis of Chiral 1,3-Oxazines: Stereoselective Total Syntheses of (+)-1-Deoxygalactonojirimycin and (-)-1-Deoxygulonojirimycin.

This paper describes the stereoselective total syntheses of (+)-1-deoxygalactonojirimycin and (-)-1-deoxygulonojirimycin via new chiral building blocks syn,anti,syn-oxazine 11a and syn,syn,anti-oxazine 13a. These were accomplished in four steps in 44.1 and 33.7% overall yields, respectively. These chirons were derived from the stereoselective addition of a nucleophile to the corresponding aldehydes of syn,anti-oxazine 10 and syn,syn-oxazine 12. Furthermore, this paper describes the stereochemical analysis of three types of chiral 1,3-oxazines; anti,syn-, syn,anti-, and syn,syn-oxazines using the NOESY technique.

Chirality extension of an oxazine building block en route to total syntheses of (+)-hyacinthacine A2 and sphingofungin B.

Concise and stereocontrolled syntheses of (+)-hyacinthacine A2 and sphingofungin B were achieved via a diastereomerically enriched oxazine intermediate. The key strategies include palladium(0)-catalyzed intramolecular oxazine formation and diastereoselective nucleophilic addition to an aldehyde. (+)-Hyacinthacine A2 was synthesized in 13 steps and 10.2% overall yield and the synthesis of sphingofungin B proceeded in a linear sequence over 15 steps and 6.9% overall yield from (R)-methyl 2-benzamido-3-((tert-butyldimethylsilyl)oxy)propanoate.

Asymmetric synthesis of (-)-swainsonine.

We report a new asymmetric synthetic method for (-)-swainsonine utilizing a chiral oxazoline precursor. The key features in this strategy are the diastereoselective oxazoline formation reaction catalyzed by palladium(0), diasteroselective dihydroxylation, and the stereocontrolled allylation reaction with TiCl(4).

Stereoselective synthesis of (+)-polyoxamic acid based on the synthesis of chiral oxazine.

A concise, stereocontrolled synthesis of (+)-polyoxamic acid was achieved. Starting from trans-oxazoline as a chiral building block, the key step involves diastereoselective oxazine formation catalyzed by palladium(0).

Application of Pd(0)-catalyzed intramolecular oxazine formation to the efficient total synthesis of (-)-anisomycin.

The enantioselective total synthesis of (-)-anisomycin, a potent antibiotic agent, has been achieved. The key steps are a Pd(0)-catalyzed stereoselective intramolecular oxazine formation from d-tyrosine and pyrrolidine formation by catalytic hydrogenation of the oxazine.

Stereoselective synthesis of L-threo-sphingosine, L-threo-sphinganine, D-threo-sphingosine, and D-threo-sphinganine via oxazoline formation and olefin cross-metathesis; potent protein kinase C inhibitor analogues.

In this study, we explored a convenient and concise route for synthesis of L-threo-sphingosine, D-threo-sphingosine, L-threo-sphinganine and D-threo-sphinganine from commercially available L- or D-serine. The key steps are the simple preparation of trans-oxazoline and intermolecular olefin cross metathesis.

A concise synthesis of a promising protein kinase C inhibitor: D-erythro-sphingosine.

In this study, we explored a convenient and concise route for synthesis of D-erythro-sphingosine 1 from commercially available and cheap L-serine. The key steps are simple preparation of amino ketone 5 from Weinreb amide 3 and high diastereoselective reduction of amino ketone 5 to give the natural erythro-(anti-) isomer.

Diastereoselective synthesis of polysubstituted pyrrolidinone as a key intermediate for the anticancer agents by palladium(II)-catalyzed carboxylation.

Palladium(II)-catalyzed carboxylation of chiral olefins 6a-d has been examined under various conditions. In the weak basic condition (K2CO3), 7a-d were obtained in good yields. Alternatively, in the strong basic condition, pyrrolidinones 8a-d were obtained resulting in excellent yields and with high diastereoselectivity.

Synthesis of 2,3-disubstituted indole on solid phase by the Fischer indole synthesis.

2,3-Disubstituted indoles were synthesized by solid-phase reaction using the Fischer indole synthesis. A "traceless" silicon linker was employed with the silicon-carbon bonding being cleaved with TFA. An oxygen atom was placed into the middle of the spacer/linker so as to enhance solid-phase synthesis by better solvation.

Diastereoselective synthesis of anti-1,2-aminoalcohol by palladium(II) catalyzed aza-Claisen rearrangement.

In this study, a highly diastereoselective synthesis of anti-1,2-aminoalcohol was explored starting from L-amino acids as chiral sources. The higher yield and diastereoselectivity was shown when the aza-Claisen rearrangement was performed with allylic trichloroacetimidate 6a in the presence of palladium(II) catalyst.

Total synthesis of sphingofungin F.

[reaction: see text] A concise, stereocontrolled synthesis of sphingofungin F was achieved. Key features involve diastereoselective oxazoline formation catalyzed by palladium(0), MgBr(2)-promoted gamma-alkoxy allylic stannane addition, and palladium(0)-catalyzed coupling of a vinyl iodide with an organozinc reagent.

Stereoselective syntheses of (+/-)-epibatidine analogues.

Stereoselective syntheses of (+/-)-epibatidine analogues 2, which contain the 8-azabicyclo [3.2.1]octane ring system, were achieved by using palladium-catalyzed cross-coupling reaction from 4 and the analgesic activity was tested by Mouse writhing antinociceptive assay.

Syntheses of (+/-)-homoepibatidine analogues.

Syntheses of (+/-)-homoepibatidine analogues (2), which contain the 8-azabicyclo [3.2.1]octane ring system, were achieved by using palladium-catalyzed reductive-coupling reaction from 3 and the analgesic activity was tested by Mouse writhing antinociceptive assay.