The Soyuz-L was a derivative of the original Soyuz rocket featuring the reinforced first stage and boosters supporting the Molniya-M's third stage, so that it could carry a more massive payload.
The Soyuz-L was essentially a two-stage derivative of the Molniya-M, itself derived from the original Soyuz. It featured the reinforced first stage and boosters used to provide support for the Molniya's third stage, allowing it to carry a larger and more massive payload.