Asymmetric synthesis of penostatins A-D from L-ascorbic acid.

The first asymmetric synthesis of (-)-penostatins B and D and the practical synthesis of (+)-penostatins A and C have been accomplished through a flexible strategy. The features of the synthesis are a BF·OEt-mediated Diels-Alder reaction of chiral dienophiles and methylcyclopentadienes with high chemo-, regio-, and stereoselectivity, followed by ozonolysis to install the common trisubstituted cyclopentane intermediate, and a hetero-Diels-Alder reaction with easily tunable facial selectivity, followed by sulfonate elimination to construct both enantiomeric tricyclic systems for penostatins A/C and B/D, respectively.

Enantioselective Total Synthesis of (+)-Penostatins A and C.

A stereoselective and column-economic approach to (+)-penostatins A and C has been developed. The multisubstituted A ring and B/C rings in their unique tricyclic framework are constructed through a Diels-Alder reaction/ozonolysis sequence and an intramolecular hetero-Diels-Alder reaction with high chemo-, regio-, and stereoselectivity. Using this route, (+)-penostatins A and C can be synthesized in 19 and 20 steps, respectively, with a good overall yield involving only five or six column chromatographic purifications.

A Synthetic Approach to Several C7-Carbasugars via a Key Intramolecular Morita-Baylis-Hillman Reaction.

A new synthetic strategy for C7-carbasugars is developed via an intramolecular Morita-Baylis-Hillman reaction, in which a substituted dial precursor prepared from d-mannose cyclizes smoothly in the presence of DMAP to afford polyhydroxylated cyclohex-1-enecarbaldehyde with good yield. By employment of the cyclization products as key intermediates, the first syntheses of carbasugar ester and epicorepoxydon A, as well as practical syntheses of epoxydines B and C, (-)-MK7607, (-)-streptol, and (-)-gabosine E are achieved.

Practical synthesis of ECH and epoxyquinols A and B from (-)-shikimic acid.

An efficient synthesis of ECH, epoxyquinols A and B, and two bioactive analogs EqM and RKTS-33 has been completed starting from (-)-shikimic acid. Rapid establishment of the desired epoxyquinol core is facilitated through a key allylic oxidation with high stereoselectivity, which is achieved by fine tuning the cyclohexene substrate structure and reaction conditions.