Most economics majors take intermediate micro and macro during their sophomore year, but some qualify to take intermediate courses during their first year. To take intermediate economics without first taking introductory economics, your personal placement must be for an intermediate course or you must have permission of the DUS.
In the fall semester, intermediate micro is offered in two formats. Econ 121 is the standard intermediate micro course. Econ 125 covers more theoretical material and is intended for students with a stronger math background. Econ 121 is also offered in the spring.
In the spring semester intermediate macro is offered in two formats. Econ 122 is the standard intermediate macro course. Econ 126 covers more theoretical material and is intended for students with a stronger math background. Econ 122 is also offered in the fall but only for sophomores and upper-classmen. No student may enroll in intermediate macro until they have taken a micro course at Yale.
All of these intermediate courses have not only introductory economics pre-reqs but also math pre-reqs. This underlines the importance of taking both introductory economics and a Yale math course during first year.