I 've got a remark, concerning the benzoyl amine protection and the use of that polyphosphoric acid in the next step.
The use of polyphosphoric acid in the synthesis of alpha-tetralone is well established, but the reaction conditions are pretty harsh ...:
Heat 120 g of polyphosphoric acid to 90 °C on a steam bad.
Liquefy 33 g of phenylbutanoic acid by heating to 70 °C and add this in one portion to the polyphosphoric acid with manual stirring. Remove the beaker from the steam bath and continue stirring for 3 minutes; the temperature should remain at about 90 °C. Then add 100 g more of polyphosphoric acid and warm on a steam bath for 4 minutes.
After workup, the yield is 79 %.
So, what's the problem? Well, I fear that these reaction conditions could remove the benzoyl protection. I bet the yield with the acyl chloride is higher & the reaction conditions aren't so harsh.
If I had to perform this synthesis, I'd use oxalyl chloride to generate the acid chloride, especially since the workup is so easy (all the side products are gasses, so you could perform the ring closure probably in the same pot).
By the way, what is the ref. for that Rabek synthesis - I 'm interested
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I understand completely that you were a bit grumpy because no bee responded to your post. In my eyes, that reaction scheme looks pretty cool. Congratulations, PrymoPyro. It really pisses me off that all the really nice posts almost get no attention. This makes you start wondering: why the hell post all those fine procedures ..., since noone seems to appreciate them.
What we are looking at is good and evil, right and wrong.