[reaction: see text] Azabicycle 4 and sec-butyllithium/TMEDA afford the C(1) bridgehead alpha-lithio anion at 0 degrees C. Anion quenching with carbon dioxide, methyl chloroformate, or DMF provide the bridgehead acid 8a (N-BOC-2,4-methanoproline), ester 8b, or aldehyde 8c, respectively. By contrast, at -78 degrees C these same reagents give a mixture of regioisomeric methylene and bridgehead anions
[反应:参见文本] Azabicycle 4和
仲丁基锂/ TME
DA在0℃下提供C(1)桥头α-
硫代阴离子。用
二氧化碳,
氯甲酸甲酯或
DMF淬灭的阴离子提供桥头酸8a(N-BOC -2,4-甲基脯
氨酸,酯8b或醛8c。相反,在-78℃下,这些相同的试剂给出区域异构的亚甲基和桥头阴离子的混合物,其猝灭分别导致区域异构的亚甲基和桥头酸6a / 8a,酯6b / 8b或醛6c / 8c的混合物。制备之前未知的3,5-甲基脯
氨酸作为其N-BOC甲酯6b。