Probably Not.

Smaug might be capable of destroying Dol Guldor but not The Black Tower of Baradur . This because this tower was made from the power of the Ring and the Ring Must be destroyed to destroy Barad Ur.

Now , at the end of the second age The Elves and Men did manage to destroy the tower but not its foundations. How the elves managed to do that I have no idea.

Secondly, Baradur is made from 'Adamant' .I have no idea what this might be, but evidently it's very tough ( possibly similar to the Orthanc Tower. The Ents could barely make a scratch on it! ) .

Smaug destroyed Lake Town using his Fire, and since the whole town was made of Wood, it was easily destroyed. The same case may be for Dale. He conquered the Lonely Mountain but he couldn't destroy it. His fire has no effect on Rocks and Stones.

Since Barad Ur is also made from a material similar to stone, his fire would have no effect on Baradur ( which in itself is a Tower of Fire ) . He might not be capable of destroying Baradur using his tail either ( assuming that it's made from the same material as Orthanc which is literally indestructible ).

Moreover, Saron had many fell creatures ( such as Balrags ) under his sway that could have easily defeated Smaug

Probably Not.

Smaug might be capable of destroying Dol Guldor but not The Black Tower of Baradur . This because this tower was made from the power of the Ring and the Ring Must be destroyed to destroy Barad Ur.

Now , at the end of the second age The Elves and Men did manage to destroy the tower but not its foundations. How the elves managed to do that I have no idea.

Secondly, Baradur is made from 'Adamant' .I have no idea what this might be, but evidently it's very tough ( possibly similar to the Orthanc Tower. The Ents could barely make a scratch on it! ) .

Smaug destroyed Lake Town using his Fire, and since the whole town was made of Wood, it was easily destroyed. The same case may be for Dale. He conquered the Lonely Mountain but he couldn't destroy it. His fire has no effect on Rocks and Stones.

Since Barad Ur is also made from a material similar to stone, his fire would have no effect on Baradur ( which in itself is a Tower of Fire ) . He might not be capable of destroying Baradur using his tail either ( assuming that it's made from the same material as Orthanc which is literally indestructible ).

Moreover, Sauron had many fell creatures ( such as Balrogs ) under his sway that could have easily defeated Smaug .

EDIT : It isn't difficult to slay a dragon. Elven warriors slew dragons throughout the first age ( notably Earendil < Ancalagon ) .If an Elf can slay a dragon, it must be a breeze for Sauron.