Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals

2,3-Butanediacetal derivatives were used for the stereoselective synthesis of unsymmetrically substituted cis-epoxides. The procedure was applied for the preparation of both enantiomers of disparlure and monachalure, the components of the sex pheromones of the gypsy moth (Lymantria dispar) and the nun moth (Lymantria monacha) using methyl (2S,3R,5R,6R)-3-ethylsulfanylcarbonyl-5,6-dimethoxy-5,6-dimethyl-1,4-dioxane-2-carboxylate as the starting material.

Total synthesis studies on macrocyclic pipecolic acid natural products: FK506, the antascomicins and rapamycin

This chapter derives its inspiration from the challenges presented to total synthesis chemists, by a particular group of macrocyclic pipecolic acid natural products. Although there is considerable emphasis on the completed syntheses of the main characters (FK506 (1), the antascomycins (4 and 5) and rapamycin (7)), the overall complexity of the molecular problem has stimulated a wealth of new knowledge, including the development of novel strategies and the invention of new synthetic methods. The ingenious and innovative approaches to these targets have enabled new generations of analogues, and provided material to further probe the biology of these fascinating molecules. With pharmaceutical application as an immunosuppressant, as well as potential use for the treatment of cancer and neurodegenerative diseases, this family of natural products continues to inspire new and interesting science while providing solutions to healthcare problems of the world.

Total Synthesis of Potent Antifungal Marine Bisoxazole Natural Products Bengazoles A and B

The bengazoles are a family of marine natural products that display potent antifungal activity and a unique structure, containing two oxazole rings flanking a single carbon atom. Total syntheses of bengazole A and B are described, which contain a sensitive stereogenic centre at this position between the two oxazoles. Additionally, the synthesis of 10-epi-bengazole A is reported. Two parallel synthetic routes were investigated, relying on construction of the 2,4-disubstituted oxazole under mild conditions and a diastereoselective 1,3-dipolar cycloaddition. Our successful route is high yielding, provides rapid access to single stereoisomers of the complex natural products and allows the synthesis of analogues for biological evaluation.

A Fascination with 1,2-Diacetals

1,2-Diacetals are readily prepared, rigid structural motifs that provide a wide range of opportunities for applications in natural product assembly. These uses encompass selective 1,2-diol or alpha-hydroxy acid protection, enantiotopic recognition and desymmetrization methods, chiral memory applications, and reactivity control in oligosaccharide synthesis, as well as functioning as templating components, chiral auxiliaries, and building blocks. 1,2-Diacetals are often more stable and lead to products with enhanced crystallinity compared to their five-ring acetonide counterparts. Many 1,2-diacetals have favorable NMR parameters, which facilitate structural assignment, particularly during asymmetric reaction processes.

Triol protection with 6-benzoyl-3,4-dihydro-(2H)-pyran

6-Benzoyl-3,4-dihydro-(2H)-pyran will protect 1,2,3-triols such as glycerol as their corresponding spiro-[5-phenyl-3,6,8-trioxabicyclo[3.2.1]octane-4,2[prime or minute]-tetrahydropyran]s and 1,2,4-triols (less efficiently) as the corresponding trioxabicyclo[3.2.2]nonanes; the hexol mannitol is converted into the corresponding bis-protected product.

Preparation of enantiopure butane-2,3-diacetals of glycolic acid and alkylation reactions leading to α-hydroxyacid and amide derivatives

The preparation of butane-2,3-diacetal protected glycolic acid and related systems is described together with highly selective alkylation reactions of (R,R) and (S,S) butanediacetal protected glycolic acid. These compounds are readily deprotected to give enantiopure alpha-hydroxyacids, alpha-hydroxyesters or alpha-hydroxyamides by suitable choice of conditions.

1,5-asymmetric induction of chirality using pi-allyltricarbonyliron lactone complexes: highly diastereoselective synthesis of alpha-functionalised carbonyl compounds

Silyl enol ethers derived from ketone functionalised rho-allyltricarbonyliron lactone complexes undergo highly diastereoselective carbon-fluorine and carbon-oxygen bond formation reactions with excellent control at the alpha-stereogenic centre.

Chiral C(2)-symmetric ligands with 1,4-dioxane backbone derived from tartrates: syntheses and applications in asymmetric hydrogenation

Chiral 1,4-diphenylphosphines 5-7 as well as thioether 8 were synthesized from tartrates employing Ley's "BDA" and "Dispoke" methodologies as the key step. Rhodium(I) complexes with 5-7 are efficient catalysts for the asymmetric hydrogenation of beta-substituted enamides and MOM-protected beta-hydroxyl enamides, which furnished chiral amines or beta-amino alcohols with 94-->99% ee. These results indicated that the 1,4-dioxane backbone in the ligands having the general structure 2 played an important role in stabilizing metal-ligand chelate conformation. Higher enantioselectivities with ligand 2 were achieved compared with the analogous ligands having the general structure 1.

The total synthesis of (+)-aspicilin using 2,3-butane diacetal protected butane tetrols via a chiral memory protocol

The total syntheses of the polyhydroxylated macrolactone (+)-aspicilin and a diastereoisomer have been achieved via a concise route, starting from the spatially desymmetrized (R',R',R,S)-2,3-butanediacetal-protected butane tetrol 13. The key steps include a regioselective silyl protection of 13 and a stereoselective Lewis acid mediated addition of allyltributylstannane to the equatorially disposed aldehyde of 4. Macrocyclization is achieved using ring closing metathesis, after which selective hydrogenation and protecting group removal yields the natural product.Key words: aspicilin, butanediacetal, desymmetrization, macrolactone, metathesis.