Further details are needed. What alkyl/aryl bromide substrates are being treated with BuLi. How are you drying the THF (LiAlH4, TPM; Na, benzophenone; other)? Is the lithiation working (i.e., you are recovering C-H versus starting C-Br) and the formylation failing?

Sir I dried THF using sodium metal and benzophenone followed by vacuum distillation and after distillation I stored THF in 3A mol seives which was dried overnight at oven. My substrate has phenolic Br group with methoxy substituents on ortho to Br of phenolic group and I have to use DMF as formulating agent according to some previous papers they dried dmf using BaO but here in India i couldn't afford it as there were no suppliers, so I added CaH2 and allow it to absorb moisture of dmf for near to 30mins ( as dmf with CaH2 on heating can decompose dmf to Dimethyl amine and CO) and I used syringe filter and carefully filtered out dmf into solvent container stored with dried 3A molecular seives with continuous purging of Argon gas to avoid moisture contact . This time after all these steps i carried out my reaction and my reaction was successful but still the yield is extremely low. Is there any way to improve my yield sir ?

The substrate being lithiated is 1,3-dimethoxy-2-bromobenzene? The paper linked to below shows that this reaction can be carried out in ether at RT. Of course, THF requires low T to avoid decomposition into ethylene and acetaldehyde enolate. Perhaps, the formylation with DMF also works better at low T, though RT DMF based formylations of alkyllithiums/aryllithiums are well known. I assume you are working from a known procedure.

https://www.ias.ac.in/article/fulltext/jcsc/093/04/0625-0634

“Halogen metal exchange of 4-bromo-l,3-dimethoxy benzene in ether solution:

To a stirred solution of 4-bromo-l,3-dimethoxy benzene (2.17 g, 0"01 mole) in ether (50 ml) was added a solution of n-BuLi (0"015 mole) in ether (80 ml). The reaction mixture was stirred for 4 hr.”

I have had the best success taking dry THF directly from a solvent still with a dried syringe (flush the syringe with a little dry THF to be certain it is completely dry). Keep slight positive overpressure on the still using a dry argon filled balloon attached to a syringe needle. Maybe also flush out the glassware (assumed to be pre-dried) with a little dry THF. Drying DMF is a challenge. Vacuum distillation from dried 4 Angstrom molecular sieves usually works. Of course, all the glassware needs to be rigorously dried. I appreciate the challenge of working under completely anhydrous conditions in a hot & humid area. Best of luck with hope the yield continues to improve.

Have you considered direct deprotonation (see attached)?

https://doi.org/10.1016/S1460-1567(02)80033-2

Regards, MDG