Question: Is it possible for sun to come in between earth and moon ?

Like an eclipse when earth comes in between Sun and moon or when moon comes in between sun and earth .

What are conditions for Sun to come in between earth and moon ?

Answer: 
The diameter of the sun is 1,391,400 km and the moon is an average of 384,400 km away, so it doesn't fit in. 

You could ideally do it if the sun becomes a black hole: the sun has a [Schwarzschild radius](https://en.wikipedia.org/wiki/Schwarzschild_radius) of approximately 3.0 km, but gravitational forces make the system very unstable. 

It is more likely that the moon will go beyond the sun, but you need at least $1.7847\*10^{20}N$ to get the moon out of the orbit.
I do not think it is possible if not artificially.
No.

The Sun is 1.3914 million km in diameter, and it's spectacularly massive, containing 99.9% of the mass of the solar system.

Everything in the solar system moves relative to the Sun, the Earth **cannot** keep on it's current track while the Sun moves to intercept the earth.

If the Sun were to be influenced by a passing black-hole, the earth would also be influenced and pulled along with the Sun.

Also consider Mercury is 57.9 million kilometers from the Sun, if we were to pass even this close to the Sun it would mean the stripping of our atmosphere and the end of all life on the planet, long before we got that close.

Also the distance between the earth and the moon is 0.38 million kilometers, which is roughly one third of the width of the Sun, so the Sun literally cannot fit between the moon and earth.

So for many many reasons, no this can't work.