Sigmatropic Rearrangement of Ammonium Ylides—Key Step in the Synthesis of Methyl 2-Formylphenyl Acetate

Abstract

N-Cyanomethyl-N,N-dimethyl-N-(α-methoxycarbonyl)benzylammonium salts 5 were synthesized and treated with different base/solvent systems, giving the products of sigmatropic rearrangements [2,3] 7 and [1,2] 8. In reactions carried out in liquid ammonia, [2,3] rearrangement definitively prevailed. Pure 7(or mixture of 7 and 8) were deprotected to afford methyl 2-formylphenyl acetate (9) in good yield.

Keywords:

• Ammonium salts
• ammonium ylides
• methyl 2-formylphenyl acetate
• sigmatropic rearrangement

Notes

^a Estimated by GC in crude reactions mixtures.

^b Yield of a crude mixture of 7 and 8.

^c Results obtained in 12–15 experiments.

^d Unidentified impurity formed in ca. 1–6% was removed under vacuum (ca. 20 °C/0.05 Torr).

^e In some experiments 2–4% of aldehyde 9 was formed.

^f Results obtained in three experiments.

^g Results obtained in six experiments.