The invention relates to compounds of formula I:where a, R1, and R3-6are as defined in the specification, or a pharmaceutically acceptable salt thereof. The compounds of formula I are serotonin and norepinephrine reuptake inhibitors. The invention also relates to pharmaceutical compositions comprising such compounds； methods of using such compounds； and process and intermediates for preparing such compounds.本發明係關於一種式I化合物：其中a、R1及R3-6係如本說明書中所定義，或其醫藥學上可接受之鹽。式I化合物為血清素及去甲腎上腺素再吸收抑制劑。本發明亦係關於一種包含該等化合物之醫藥組合物；使用該等化合物之方法；及製備該等化合物之方法及中間物。
