New, highly efficient syntheses of rac-, (R)- and (S)-4-hydroxy-2-cyclohexenone

Chemoenzymatic preparation of optically active cyclic 4-hydroxy-acylaziridines

A highly enantioselective chemoenzymatic route to cyclic 4-hydroxyacylaziridines is described.

Formal enantioselective syntheses of oseltamivir and tamiphosphor

An alternative and expedient route for the synthesis of the influenza antiviral drugs oseltamivir and tamiphosphor is described.

An Enantioselective Approach to 4-O-Protected-2-cyclopentene-l,4-diol Derivatives via a Rhodium-Catalyzed Redox-Isomerization Reaction

Kinetic resolution of a series of cyclopentene-1,4-diol derivatives has been successfully achieved with enantiomeric excess up to 99.4% and a kf/ks ratio of 55 by a rhodium-catalyzed redox-isomerization reaction in a noncoordinating solvent.

Enantioselective Synthesis of Natural Polyoxygenated Cyclohexanes and Cyclohexenes from [(p-Tolylsulfinyl)methyl]-p-quinols

Exploitation of the beta-hydroxysulfoxide fragment present in a number of enantiomerically pure (SR)- and (SS)-[(p-tolylsulfinyl)methyl]-p-quinols allowed chemo- and stereocontrolled conjugate additions of different organoaluminium reagents to the cyclohexadienone moiety. The same fragment was also shown to act as an efficient chiral masking carbonyl group, after oxidation to sulfone and retroaddition in basic medium, with elimination of methyl p-tolyl sulfone. Through the use of both transformations as key steps, enantiocontrolled syntheses of different natural products-such as the two enantiomers of dihydroepiepoformin, (-)-gabosine O, (+)-epiepoformin, (-)-theobroxide and (+)-4-epigabosine A (an epimer of the natural product gabosine A)-has been achieved. The presence of the beta-hydroxy sulfone moiety makes the cyclic structures rigid, allowing a number of stereoselective transformations such as carbonyl reductions, enone epoxidations or cis-dihydroxylations, en route to the natural structures. The observed selectivities were dependent on the particular substitution in each substrate, providing evidence of a strong influence of remote groups on the preferred approach of the reactants to the reactive conformations. An advanced precursor of natural (+)-harveynone was also synthesized, but the isolation of the natural product was not possible because of the instability of the corresponding enone, containing a triple bond, under the basic conditions necessary to eliminate the beta-hydroxy sulfone. This demonstrated that the limitations of the use of the beta-hydroxy sulfoxide as a chiral protecting carbonyl group were dependent on the relative stabilities of the final targets in the presence of the required base.

Enantioselective Synthesis and Absolute Configuration Assignment of Gabosine O. Synthesis of (+)- and (−)-Gabosine N and (+)- and (−)-Epigabosines N and O

[reaction: see text] A rational approach to the synthesis of gabosines and other related carba-sugars starting from a masked p-benzoquinone has been designed. The enantioselective acetylation of the hydroxyketal 2 provides a practical entry to either enantiomer of the target products. The strategy has been applied to the synthesis of (+)- and (-)-gabosines N and O and (+)- and (-)-epigabosines N and O. The absolute configuration of natural gabosine O has been established.

Diastereoselective dearomatization of resorcinols directed by a lactic acid tether: unprecedented enantioselective access to p-quinols

An operationally simple oxidative dearomatization of resorcinol derivatives is reported that employs an inexpensive chiral directing group. The method provides access to a variety of p-quinol derivatives in good yield and diastereoselectivity. A short reductive process affords 4-hydroxy-4-alkylcyclohexenone derivatives in excellent yields and enantiomeric excesses.

A new and efficient chemoenzymatic route to both enantiomers of 4-hydroxycyclohex-2-en-1-one

[reaction: see text] A chemoenzymatic synthesis of both enantiomers of the pharmacologically interesting 4-hydroxycyclohex-2-en-1-one in three steps starting from 3-methoxycyclohex-2-en-1-one is described. Manganese(III) acetate-mediated acetoxylation followed by enzyme-mediated hydrolysis of alpha-acetoxy enone affords acetoxy enone 3 and hydroxy enone 4 with high enantiomeric excesses and in good yields. The reduction of the acetoxy and hydroxy enones furnished both enantiomers of 4-hydroxycyclohex-2-en-1-one in high enantiomeric excess.