An efficient general method for the construction of chiral α-acetylene alcohols has been developed. The new method consists of the Katsuki-Sharpless asymmetric epoxidation of allylic alcohol substrates, conversion of the chiral epoxides into the corresponding chloro-epoxides, and brief exposure of the latter products with an excess n-butyllithium in tetrahydrofuran. The reaction leads to the formation of the corresponding terminal α-acetylene alcohols readily in excellent yields without affecting original chiral integrities introduced in the asymmetric epoxidation reaction. Employing the new chiral α-acetylene alcohol formation reaction as the key step as well as using a chiral acetylene alcohol thus generated as a common building block, some isoprenoid natural products ranging from mevalonolactone to α-tocopherol have been synthesized in an enantiocontrolled sequence of reactions. Namely, a single acetylene alcohol obtained has been sequentially elongated via a monoterpenoid citronellal, a sesquiterpenoid perhydrofarnesol, and a diterpenoid phytol by iterative application of the key reaction to complete a linear synthesis of α-tocopherol. On the other hand, the same acetylene alcohol has been separately transformed into the two known segments, chromanethanol and the perhydronor-farnesol, to complete a convergent synthesis of α-tocopherol. During these transformations, an isoprenoid biogenetic precursor mevalonolactone, olfactive monoterpenoids, linalool, cis- and trans-rose oxides, and an irregular phenolic monoterpenoid bakuchiol have been synthesized from the same acetylene alcohol in enantiocontrolled ways.
