Kunio Ogasawara

Extremely Facile and Selective Nickel-Catalyzed Allyl Ether Cleavage

Childs play! Allyl ethers as protecting groups for hydroxyl functions can be removed readily with a combination of DIBAL and catalytic amounts of [NiCl2 (dppp)]. Propene is expelled in this remarkably selective reaction, and a nickel-catalyzed hydroalumination-elimination pathway is proposed [Eq. (a)]. dppp=propane-1,3-diylbis(diphenylphosphane).

Facile and specific nickel-catalyzed de-N-allylation

Abstract A general procedure for a chemoselective removal of the allyl (2-propenyl) functionality on basic, neutral and acidic nitrogens by diisobutylaluminum hydride or trimethylaluminum in the presence of a catalytic amount of (dppp)NiCl2 has been developed.

A new chiral route to 5- and 6-substituted hydropyran-2-ones utilizing enantiopure 4-cumyloxy-2-cyclopenten-1-one

Abstract Starting from enantiopure 4-cumyloxy-2-cyclopenten-1-one, a route to 5- and 6-substituted hyropyran-2-ones has been developed. The method has achieved the synthesis of 4,5- cis - and 4,5- trans -5-ethyl-4-hydroxytetrahydropyran-2-ones assigned to marine natural products simplactones A and B to disprove the former and revise the latter of the proposed structures.

Asymmetric synthesis of sceletium alkaloids: (−)-mesembrine, (+)-sceletium A-4, (+)-tortuosamine and (+)-N-formyltortuosamine

Abstract Three procedures for the transformation of achiral 1-(3,4-dimethoxyphenyl)-cyclohexene into enantiomerically pure 2-(3,4-dimethoxyphenyl)cyclohex-2-en-1-ol have been established at first. Utilizing the (−)-cyclohexenol thus obtained, the four titled Sceletium alkaloids have been synthesized in the natural enantiomeric forms.

Asymmetric hydrogen transfer protocol for a synthesis of (+)-frontalin and (−)-malyngolide

Abstract An insect aggregate pheromone (+)-frontalin and a marine antibiotic (−)-malyngolide, both bearing a quaternary stereogenic center in their molecules, have been synthesized in diastereocontrolled manner by employing a catalytic asymmetric hydrogen transfer reaction as the key step. An inversion protocol allowing enantioconvergent use of the other enantiomeric resolved product has also been devised.

A concise synthesis of (−)-neplanocin A

Abstract A concise stereocontrolled route to (−)-neplanocin A, a naturally occurring carbocyclic nuleoside, has been developed by employing lipase-mediated kinetic resolution.

A new tactic for diastereo- and enantiocontrolled synthesis of (−)-malyngolide via catalytic meso-asymmetrization

Abstract A meso -1,4-enediol bis -silyl ether 2 having bicyclo[2.2.1]heptene background has been transformed diastereo- and enantioselectively into (−)-malyngolide 1 , an antibiotic isolated from the blue-green marine algae, Lyngbya majuscula , via Rh(I)-( R )BINAP-catalyzed asymmetrization and diastereoselective modification of the optically active product thus obtained.

A diastereocontrolled route to the tetrahydropyran nucleus of pseudomonic acids

Abstract A diastereocontrolled synthesis of the tetrahydropyran nucleus of pseudomonic acids has been achieved starting from a chiral building block, which we have developed. The key step is a convex-face reduction of the block having a biased framework which allowed assemblage of the most important core in a completely diastereoselective manner.

A furan route to (−)-exo-isobrevicomin

Abstract A new enantiocontrolled synthesis of (−)- exo -isobrevicomin, isolated from male mountain pine beetles, Dendroctonus ponderosae , has been established starting from 5-ethyl-2-furfural by employing AD-mix-induced asymmetric induction and oxidative furan ring-expansion reaction as the key steps.

A convenient enantioselective synthesis of natural (1R,3S)-amidinomycin.

Abstract Natural (1 R ,3 S )-amidinomycin, an antiviral metabolite isolated from Streptomyces species, has been synthesized conveniently from (+)-norcamphor in an enantioselective manner.