Oxazine anions, reaction with alkyl halides

Hydrolytic reactions can also be applied in the synthesis of aldehydes or ketones via the corresponding 1,3-oxazine derivatives. The anion formed from 3-methyl-2-(4-pyridyl)tetrahydro-l,3-oxazine 155 on treatment with BuLi proved to react with various electrophiles (alkyl halides, carboxylic esters, acid chlorides, or aldehydes) exclusively at position 2 of the 1,3-oxazine ring and not at the pyridine nitrogen atom. The readily formed 2,2-disubstituted-l,3-oxazine... 

Dihydro-2-fluoromethyl-4,4,6-trimethyl-4/f-l,3-oxazine (86) can be deprotonated by treatment with butyllithium, and the anion then reacted with electrophiles such as alkyl halides and carbonyl compounds. Reduction and hydrolysis of the products destroy the heterocycle and releases the corresponding a-fluoroaldehydes. For example, reaction of the anion with 3-chloropropene yields the fluorobutenyl-l,3-oxazine (87), which on reduction and hydrolysis yields 2-fluoropent-4-enal (88) (Scheme 19) <90TL179>. 

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