32 グリセルアルデヒド誘導体を基質とするヘテロヨヒンビンアルカロイドのキラル合成

抄録

Four chiral bicyclic lactone carbamates (11)-(14), potential synthons for the synthesis of the heteroyohimbine type indole alkaloids, are prepared in highly selective manners from a single chiral precursor diethyl L-tartrate by employing the intramolecular hetero-Diels-Alder reaction with inverse electron demand as a key step. Thus, we develop a selective way for the modification of diethyl L-tartrate to give the isomeric threitol derivatives (16) with E olefin and (17) with Z olefin which then are oxidatively converted into the glyceladehydes derivatives (20) and (24), respectively. Condensation of the former with Meldrum's acid yields the tricyclic lactone (22) with cis ring juncture selectively by spontaneous intramolecular hetero-Diels-Alder reaction, on the other hand, the latter affords the tricyclic lactone (5b) with trans ring juncture selectively under the same conditions. We can conclude that the stereochemistry of the adducts is directed by the configuration of the dienophile moiety. Conventional chemical transformation allows the formation of the key intermediates (13) and (14) from (22), while (11) and (12) from (5b) without difficulties.