Additionally, the Red Sox chose right-hander Brian Keller in the second round from the Yankees’ Double-A Somerset roster.
Jennings, 23, owns a career 19-19 record with one save and a 4.75 ERA in 79 games (51 starts) over four Minor League seasons (2017-19, ’21).
The Brush Creek, Tenn., native combined to go 9-1 with one save, a 4.99 ERA and 59 strikeouts in 74 innings over 29 appearances (one start) this past season for Low-A Bradenton, High-A Greensboro and Double-A Altoona.
Pittsburgh originally selected Jennings in the second round (42nd overall) of the 2017 MLB Draft.
The 22-year-old Ramírez -- who is not related to the slugger of the same name who mashed 555 home runs in the big leagues -- has gone 3-5 with a 4.33 ERA in 35 games (14 starts) over three Minor League seasons (2017-19).
Ramírez, who did not pitch in 2021 due to injury, has notched 126 strikeouts against 73 hits allowed and 77 walks issued in 95 2/3 innings. The Astros originally signed the Santo Domingo, D.R., native as a non-drafted free agent in July 2017.
Keller, 27, spent last season with Triple-A Scranton/Wilkes-Barre, where he went 2-2 with a 2.77 ERA in 26 games (11 starts). In 55 1/3 innings, Keller permitted 43 hits and 46 walks with 65 strikeouts. He was a 39th-round selection by the Yankees in the 2016 MLB Draft.