An efficient approach to the typeIII lepadin alkaloids (lepadins Fa nd G) has been developed throughak ey Diels-Alder reaction, in which an ovel ketolactone-type dienophile with chiral diol unit is employed to generate the desirable all-cis-trisubstituted cyclohexenew ith excellent regio-and stereoselectivity control. The subsequents elective sulfonylationo ft he diol unit followed by S N 2c yclization under hydrogenation conditions could construct the substituted piperidine ring. By using this approach, (À)-lepadin Fi ss ynthesized from ethyl l-lactate for the first time. Figure 1. Structures of lepadins A-I.

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A flexible approach to both the type II and III lepadin alkaloids is developed for the first time. A key Diels−Alder reaction based on a novel chiral ketolactone dienophile is employed to obtain the desirable all-cis-trisubstituted cyclohexene with excellent regio- and stereoselectivity. As the subsequent closure of the piperidine ring is devised at the N1 and C2 position via a intramolecular nucleophilic amination, the two stereochemical types of lepadin frameworks with the opposite configuration at C2 can be conveniently accessible from a common intermediate. By the approach, lepadins D, E (type II) and F (type III) are stereoselectively synthesized from ethyl L-lactate.

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...

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