In 1939 the senior Abwehr agent in Turkey carried out a secret survey of the route through Persia to Baku with the possibility in mind of a pre-emptive strike to seize the fields from the Soviet Union to prevent the French army in Syria doing so.
This article is worth a read too. Too Little, Too Late: An Analysis of Hitler's Failure in August 1942 to Damage Soviet Oil Production https://www.joelhayward.org/Too-Little-Too-Late.2.pdf