The Synthetic Routes of (17a,20E)-17,20-[(1-Methoxyethylidene)bis(oxy)]-3-

The synthesis of (17a,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxabicyclo[2.
2.
3]non-6-ene, also known as 6,7,19,20-tetrahydro-1H,11H-benzo[b]pyrrole-1-one, is an important synthetic route in the chemical industry.
This compound has a wide range of applications in various fields such as pharmaceuticals, agrochemicals, and cosmetics.

One of the most commonly used synthetic routes for the production of (17a,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxabicyclo[2.
2.
3]non-6-ene is through a seven-step synthesis process.
The first step in this process involves the preparation of a methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate through the reaction of 2-oxo-1,3-oxazolidine-3-carboxylic acid with methyl 2-oxo-2,3-dihydro-1H-pyrrole-1-carboxylate.

The second step involves the reduction of the methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate to form methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate using a reducing agent such as lithium aluminum hydride (LiAlH4).

In the third step, the methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate is treated with a Grignard reagent, such as methyl magnesium bromide, to form the corresponding methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate.

In the fourth step, the methyl 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-carboxylate is treated with a halogenating agent, such as thionyl chloride, to form the corresponding 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-yl chloride.

In the fifth step, the 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-yl chloride is treated with a base, such as sodium hydroxide, to form the corresponding 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-ol.

In the sixth step, the 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-ol is treated with a hydroborating reagent, such as sodium borohydride, to form the corresponding 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-one.

Finally, in the seventh step, the 2-oxo-5-oxa-bicyclo[2.
2.
3]non-6-ene-3-one is treated with a reducing agent, such as lithium aluminum hydride (LiAlH4), to remove the protecting group and form the final product, (17a,2