Treatment of the 4-silyloxy-N-Boc-L-proline methyl ester 1 with allyl bromide in the presence of LDA in THF at −78 °C gives a mixture of the (2S,4R)- and (2R,4R)-2-(prop-2-enyl)-4-silyloxy-N-Boc-L-proline esters 2a and 2b in 75% combined yield in the ratio 53 ∶ 47. In contrast, similar treatment of the (−)- and (+)-menthyl esters 5 and 6 gives a mixture of allylated products 7a,b and 8a,b in the ratio 75 ∶ 25 and 89 ∶ 11, respectively. Reaction of 6 with methyl iodide and propyl iodide also give the corresponding 2-alkylated esters 16a and 16b in a highly diastereoselective manner (94 ∶ 6 and 93 ∶ 7, respectively).
在-78°C下,将4-
硅氧基-N-
Boc-L-脯氨酸甲酯1与烯丙基
溴在
LDA和THF的存在下反应,得到了(2S,4R)-和(2R,4R)-2-(丙-2-烯基)-4-
硅氧基-N-Boc-
L-脯氨酸酯2a和2b的混合物,总产率为75%,其比例为53∶47。相比之下,类似处理(-)和
(+)-薄荷醇酯5和6则分别得到烯丙基化产物7a,b和8a,b的混合物,比例分别为75∶25和89∶11。此外,6与甲基
碘和丙基
碘反应也以高度立体选择性(分别为94∶6和93∶7)得到相应的2-烷基化酯16a和16b。