A simple procedure for the asymmetric synthesis of lignans via chiral β-benzyl-γ-butyrolactones has been developed. The key benzylbutyrolactone intermediates were efficiently synthesized using a six-step procedure, starting from 3,4-(methylenedioxy)cinnamic acid. The key step in this sequence was a highly diastereoselective alkylation of an N-acyloxazolidinone enolate. The resulting β-benzyl-γ-butyrolactones were subsequently transformed into the benzylidene lignans gossypifan and savinin (hibalactone) via aldol condensation–dehydration reactions, and into the dibenzylbutyrolactone lignan 4′-demethylyatein, through alkylation. Oxidation of 4′-demethylyatein with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) afforded cis-and trans-benzylidenebenzylbutyrolactones, whereas oxidation with DDQ/TFA gave 4′-demethyl-deoxyisopodophyllotoxin. Keywords: lignans, synthesis, asymmetric, biosynthesis, oxidation, benzylbutyrolactones.
已开发出一种通过手性β-苄基-γ-丁酰内酯的不对称合成法合成木脂素的简单程序。关键的苄丁内酯中间体通过一个六步程序高效合成,起始物为3,4-(亚甲二氧基)肉桂酸。该序列中的关键步骤是对N-酰基噁唑烷酮烯醇的高度对映选择性烷基化。随后,产生的β-苄基-γ-丁酰内酯通过醛缩脱水反应转化为苄亚甲基木脂素gossypifan和savinin(hibalactone),并通过烷基化反应转化为二苄丁内酯木脂素4'-去甲基亚特因。用2,3-二氯-5,6-二氰-1,4-苯醌(DDQ)氧化4'-去甲基亚特因得到顺和反苄亚甲基丁内酯,而用DDQ/TFA氧化则得到4'-去甲基脱氧异鬼臼毒素。关键词:木脂素、合成、不对称、生物合成、氧化、苄丁内酯。