w单杂环 ·5员杂环 失喃 噻吩 吡咯 furan thiophene pyrrole 噻唑 吡唑 咪唑 thiazole pyrazole imidazole 噁唑 异恶唑 oxazole isoxazoleO 5 1 2 4 3 5 furan S 1 2 4 3 5 1 2 4 3 5 N H thiophene pyrrole N S N N H N N 1 H 2 4 3 5 1 2 4 3 5 1 2 4 3 5 thiazole pyrazole imidazole N O O N oxazole isoxazole