David Wenham, "Paul's Use of the Jesus Tradition: Three Samples":
Not only did he know traditions of Jesus' passion and resurrection - see 1 Corinthians 11 and 15 - but also sections of the Sermon on the Mount, Peter's benediction, the dialogue about divorce and the eschatological discourse. He may well have known the woes of the scribes and Pharisees that precede the eschatological discourse in Matthew, also the controversy stories that precede the woes, and probably the mission discourse. This list could be extended, but even this amount of evidence makes it very clear that Paul knew a considerable proportion of what we know as the synoptic tradition (particularly of the material found in Matthew 19-28 and parallels).
The evidence points to Paul's familiarity with a wide range of gospel traditions - traditions attested in the different synoptic strata (so-called 'Markan', 'Q', 'M' and 'L' material) and traditions of different types, not just sayings material. (in Gospel Perspectives Volume 5, pg. 28)