A new and very direct enantioselective total synthesis of members of the β-amyrin family of pentacyclic triterpenes has been developed starting with acylsilane 5, 2-propenyllithium, and cyclohexenylmethyl bromide 6, which were assembled to form tetraene 7. Cationic cyclization of 7 and silylation afforded 8, which after vinyl triflate formation was cyclized via a Cu(I) intermediate (Scheme ) to form the TBS ether of aegiceradienol 10, a versatile intermediate that is readily converted into natural β-amyrins such as β-amyrin (1) and oleanolic acid (2). The C(14)-diastereomer (13) of aegiceradienol was also synthesized from the C(14)-diastereomer of 8 using an intramolecular Stille reaction for the closure of ring D (Scheme ).

Desogestrel (1) has been synthesized enantioselectively by a 14-step process from the known and readily available precursor 3, as outlined in Chart . At the heart of this process is the short, convergent, and stereocontrolled method for forming the tetracyclic ring system and the critical 11-exomethylene function, that is, the sequence of steps 6 → 8 → → 12. All steps of the synthesis proceed in good yield.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.