Sapronov was expelled from the party at the fifteenth Party Congress in December 1927 with the rest of the inner party opposition and was deported to the Crimea. The circumstances of his capitulation to Joseph Stalin in 1928 remain unclear but he was rearrested in 1932 and spent the rest of his life in prison, most notably in the notorious Verkhneuralsk isolator. He was sentenced to death on 28 September 1937 and executed the same day.