An Efficient Formal Synthesis of (−)-Balanol by Using Ruthenium-Catalyzed Asymmetric Hydrogenation

Asymmetric transfer hydrogenation of α-amino β-keto ester hydrochlorides through dynamic kinetic resolution

The development of Ru-catalyzed asymmetric transfer hydrogenation of α-amino β-keto ester hydrochlorides is described.

A unified approach to the important protein kinase inhibitor balanol and a proposed analogue

A common approach to the important protein kinase inhibitor (−)-balanol and an azepine-ring-modified balanol derivative has been developed using an efficient fragment coupling protocol which proceeded in good overall yield.

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

An efficient catalytic synthesis of α-amino-β-keto esters has been newly developed. Cross-coupling of various aldehydes with α-imino ester, catalyzed by N-heterocyclic carbene, leads chemoselectively to α-amino-β-keto esters in moderate to good yields with high atom efficiency. The reaction mechanism is discussed, and it is proposed that the α-amino-β-keto esters are formed under thermodynamic control.

A mild and efficient direct α-amination of β-dicarbonyl compounds using iodosobenzene and p-toluenesulfonamide catalyzed by perchlorate zinc hexahydrate

A direct α-amination of β-dicarbonyl compounds has been achieved by using iodosobenzene (PhIO) as an oxidant and p-toluenesulfonamide (TsNH(2)) as an aminating reagent in the presence of a catalytic amount of perchlorate zinc hexahydrate. The present amination reaction proceeds quickly at rt (<30 min needed for most tested substrates) to provide the corresponding α-N-tosylamido β-dicarbonyl compounds in high to excellent yields.

Highly diastereo- and enantioselective synthesis of monodifferentiated syn-1,2-diol derivatives through asymmetric transfer hydrogenation via dynamic kinetic resolution

The first enantio- and diastereoselective approach to alpha-alkoxy-substituted syn-beta-hydroxyesters through highly efficient catalytic asymmetric transfer hydrogenation via dynamic kinetic resolution reactions from the corresponding racemic beta-ketoesters is described. In this atom-economical process, two contiguous stereogenic centers are generated simultaneously with an excellent diastereoselectivity (up to 99/1) and enantioselectivity (up to 99%), allowing a rapid access to a wide variety of aromatic and heteroaromatic monodifferentiated syn-1,2-diols.

Total synthesis of (-)-balanol, all stereoisomers, their N-tosyl analogues, and fully protected ophiocordin: an easy route to hexahydroazepine cores from garner aldehydes

Total syntheses of (-)-balanol and all of its stereoisomers starting from easily available Garner aldehydes are described. Diastereoselective Grignard reactions on Garner aldehydes and ring-closing metatheses are the key steps for the construction of hexahydroazepine subunits. The benzophenone subunits were constructed through coupling of suitably functionalized aromatic aldehyde and bromo components. The synthetic route constitutes a convenient and scalable reaction sequence to generate all of the stereoisomers of balanol. The methodology is explored further for the synthesis of N-tosyl analogues of balanol and of fully protected ophiocordin.

Chiral version of the Burgess reagent and its reactions with oxiranes: application to the formal enantiodivergent synthesis of balanol

An efficient formal synthesis of a (-)-balanol intermediate ( 25a) from cyclohexadiene oxide was accomplished in eight steps. An asymmetric version of the Burgess reagent allows for an enantiodivergent approach to both enantiomers of balanol from a racemic starting material.

Recent studies on asymmetric hydrogenation. New catalysts and synthetic applications in organic synthesis

CODRu(h3methylallyl)2 is a versatile starting material for the preparation of a wide range of chiral bisphosphines ruthenium(II) complexes: (P*P)Ru(h3methylallyl)2 2, Ru[X4(P*P)2] 3, and cationic monohydride ruthenium complex 4. A facile synthesis of new C2 electron-rich chiral phosphines, bis(phosphetano)benzene 8 and 1,1¢bis(phosphetano)ferrocene 10 is presented. Dynamic kinetic resolution was used for efficient syntheses of key components of the hexahydroazepane core 16 of balanol and of optically pure Boc-(2S,3R,3S)-iso-dolaproïne 19. Catalyst 4 was used in asymmetric hydrogenation of 22 to give (+)-cis-methyl dihydrojasmonate in high enantioselectivity.

Stereoselective synthesis of iso-dolaproine via dynamic kinetic resolution

[see reaction]. An efficient multigram-scale synthesis of optically pure Boc-(2S,3R,4S)-iso-dolaproine is reported using dynamic kinetic resolution (DKR). The catalytic asymmetric hydrogenation of ethyl (4S)-3-(2'-pyrrolidinyl)-3-oxo-2-methyl propanoate hydrochloride using in situ generated Ru[(S)-MeO-BIPHEP]Br2 catalyst affords the anti beta-hydroxy alpha-methyl ester quantitatively. The two new stereogenic centers are simultaneously controlled with high diastereoselectivity.