Henry reaction with orthoformate water scavenger

[Rhodium]

Nitroalkene synthesis (Henry reaction) using trimethyl orthoformate to remove the water formed in the reaction: (MeO)₃CH + H₂O -> 2 MeOH + HCOOMe

1-(2,6-dimethoxyphenyl)-2-nitropropene

A mixture of nitroethane (3.4 g, 45 mmol), 2,6-dimethoxybenzaldehyde (7.0 g, 42 mmol), CH₃COOK (2.4 g, 35 mmol), methylamine hydrochloride (3.4 g, 35 mmol), trimethyl orthoformate (10 ml), and methanol (30 ml) was stirred at reflux for 7 h. The reaction mixture was poured into water and extracted with ethyl ether. After the usual work up, the crude product was recrystallized from MeOH-Et₂O to give 1-(2,6-dimethoxyphenyl)-2-nitropropene, 7.5 g (80%), mp 102-103°C.

Reference: Tetrahedron 46, 7483 (1990)