Did you UTFSE first, or even
think before posting?
There is a point in making the nitrosation of propenylbenzenes in a two-phase solution, and that is that the relatively acid-sensitive alkene (in the ether phase) won't have to be in contact with the acid more than necessary, and that only the N
2O
3 gas formed in the aqueous layer will bubble through the ether and react with the alkene to form the pseudonitrosite.
Using THF, the alkene will be in contact with acid during the whole reaction, and it will probably not appreciate that. I also don't believe sodium nitrite is at all soluble in THF.
DCM is not a substitute for ether either, as it is heavier than water, and won't let any formed N
2O
3 gas bubble through it. If you UTFSE, you'll see that people have tried to use petroleum ether instead of diethyl ether, and while it worked, it produced inferior results. If you read my
Pseudonitrosite FAQ
(
https://www.thevespiary.org/rhodium/Rhodium/chemistry/pseudonitrosite.html), you'll see that Toennies' method to synthesize pseudonitrosites was to add a NaNO
2 solution to a solution of the propenylbenzene in glacial acetic acid, but that method also produced lower yields.