34 シクロシトリルフェニルスルホンを用いるビタミンA関連化合物の合成

抄録

The discovery of a simple and practical method for the preparation of functionalized cyclocitryl derivatives promising versatile applications for the synthesis of naturally occurring biologically active terpenoids such as vitamin A, abscisic acid and so on has long been recieved much interests. In the last communications we demonstrated that cyclocitryl phenyl sulfone 2 was effectively prepared by acid-catalyzed cyclization of geranyl phenyl sulfone 1 and, furthermore, the sulfone 2 and its derivatives 3 and 5 could be used as key intermediates for the terpenoid syntheses. Here, we show a novel synthesis of vitamin A_1 and A_2 acids involving C_<10>-C_<10> coupling reaction between 2 or 5, and the corresponding bromo compounds 29, 30, and 33. The compounds 29, 30, and 33 were prepared in reasonable yields by the coupling of C_5 unit as shown in scheme 3. The reaction of 2 with 29 was performed in 92% yield by lithiation of 2 with (i-Pr)_2NLi followed by the action of 29 in THE at -78℃. Similarly, 19 and 20 were obtained in 67 and 68%, respectively. Finally, the base-catalyzed desulfination of 18, 19, and 20 was effected with t-BuOK in t-BuOH-THF (2: 1), yielding vitamin A acid as a mixture of trans and cis isomers on C_2 carbon.