It sure feels like something that should be related to Schanuel's conjecture.  Note that this is equivalent to finding integers $m$ and $q$ such that $$x = \frac{\ln m + 2\pi i q}{\ln 3}$$ is *not* an integer but $2^x$ is.  [$3^x$ simplifies to $m$ by construction].  

Continuing this, let us actually compute $2^x$.  If we split it into real and imaginary parts, a large messy expression ensues.  But it naturally splits into 2 reasonable cases, depending on whether $m\gt 0$ or $m \lt 0$.  Let's deal with the positive case first.  We get
$$2^x = m^{\log_3 2}\left( \cos(2q\log_3(2) \pi) + i \sin(2q\log_3(2) \pi)\right) $$
For that to be an integer, it has to at least be real, but unless $2\log_3(2)q$ is an integer, the $\sin$ term will not be $0$.  For $q=0$, this is $m^{\log_3 2}$.  We can rewrite that as $2^{\log_3 m}$.  But we assumed that $m$ was a power of $3$, so $\log_3 m$ (and thus $x$) is an integer.

For the $m \lt 0$, we get the slightly more complicated 
$$2^x = (-m)^{\log_3 2}\left( \cos(2(2q+1)\log_3(2) \pi ) + i \sin(2(2q+1)\log_3(2) \pi )\right) $$
Since $m\lt 0$, the first term is real, so we need $2 (2q+1)\log_3(2)$ to be an integer for the $\sin$ term to disappear, which cannot happen.

Can someone find a flaw in my reasoning?  I somehow expect so, as this did not seem difficult, and I would expect it to be if it's an open problem!