Hajime Yokoyama

Regioselective demethylation of 2,6-dimethoxybenzaldehydes with magnesium iodide etherate

Abstract Demethylation of asymmetically substituted 2,6-dimethoxybenzaldehydes with magnesium iodide etherate regioselectively single 6-methoxysalicylaldehydes derived from the more unstable chelation.

Total synthesis of SS20846A via intramolecular Pd(II)-catalyzed cyclization

Abstract A stereoselective total synthesis of SS20846A was efficiently accomplished by means of an intramolecular palladium(II)-catalyzed cyclization.

A new preparation of 2,5-dihydro-1-benzoxepins using Mitsunobu cyclization, and the synthesis of natural radulanins

Abstract Mitsunobu cyclization of o -[4-hydroxy-3-methyl-2( Z )-butenyl]phenol 2a effected selective seven-membered cyclization to give 3-methyl-2,5-dihydro-1-benoxepin 1a . Using this procedure, natural radulanin A and radulanin A methyl ether were synthesized effectively.

Palladium(II)-catalyzed stereocontrolled cyclization via hemiacetal intermediates: Total synthesis of 5-epi-prelactone C

Palladium(II)-catalyzed cyclization of 3,7-dihydroxy-4-methyl-5-octenal derivative was carried out to give 2,3,4,6-tetrasubstituted tetrahydropyran with stereoselective 1,3-chirality transfer in net retention of stereochemistry. The cyclized product was converted into 5-epi-prelactone C.

PALLADIUM(II)-CATALYZED CYCLIZATION OF URETHANES AND ITS APPLICATION TO A TOTAL SYNTHESIS OF 1-DEOXYNOJIRIMYCIN

We have employed a palladium(II)-catalyzed cyclization of allylic alcohol as a key reaction to achieve a total synthesis of the azasugar 1-deoxynojirimycin from D-mannitol. This reaction should be useful for the stereoselective construction of natural poly-substituted piperidine derivatives.

Regioselective cyclization of m-acylaryl 1,1-dimethylpropargyl ethers giving 5-acyl-2,2-dimethyl-2H-chromenes

Abstract Thermal cyclization of some m -acylaryl 1,1-dimethylpropargyl ethers ( 1a – f ) effected regioselective ortho cyclization giving the corresponding 5-acyl-2,2-dimethyl-2 H -chromenes ( 2a – f )

Pd(II)-Catalyzed Cyclization to Ether and Its Application to the Synthesis of the trans-Fused Polyether Core

We employed an iterative Pd(II)-catalyzed cyclization reaction to ether from tri-O-acetyl-D-glucal to synthesize trans-fused polyethers. This approach should be applicable to synthesize the core structure of marine ladder toxins.

A NEW SYNTHETIC STRATEGY FOR 2-DEOXY-D-RIBOSE VIA PALLADIUM(II)-CATALYZED CYCLIZATION OF ALDEHYDE

We achieved a total synthesis of 2-deoxy-D-ribose through intramolecular Pd(II)-catalyzed cyclization of aldehyde via an unstable hemiacetal intermediate as a key step.

A NOVEL PENTOSE SYNTHESIS VIA PALLADIUM(II)-CATALYZED CYCLIZATION OF AN UNSTABLE HEMIACETAL

PdCl 2 (PhCN) 2 (5 mol%)-catalyzed cyclization of a hemiacetal derived from (E,2S,3R)-2,3-isopropylidenedioxy-6-(tetrahydro-2H-pyran-2-yl)-4-hexenal and methanol gave substituted furanoside in moderate yield, exclusively via 5-exo-mode cyclization, without the need for a reoxidant. New stereogenic centers at C1 and C4 on the tetrahydrofuran ring showed preferential 1R and 4R stereochemistry due to anomeric effect (n o -σ * c-o ) and A 1,2 strain, respectively. This methodology was applied to stereocontrolled synthesis of pentoses: D-ribose and L-lyxose.

Asymmetric synthesis of chiral 2-fluorinated 1,3-propanediols and its application to the preparation of monofluorinated chiral synthon

Abstract Asymmetric synthesis of optically active 2-fluorinated 1,3-propanediols was achieved by enzymatical resolution and applied to obtain a chiral monofluorinated synthon for lignan derivatives.