Structure determination and synthesis of a new gibberellin, GA(99), from spinach plants: 2 beta-hydroxy-GA(19)

The structure of a new gibberellin, (GA(99), isolated from Spinach plants has been determined to be 2 beta-hydroxy-GA(19) (6) by synthesis from gibberel ic acid. The key steps in the preparation involved the reduction under Luche conditions of a Delta(1(10))-2-one derivative to furnish the critical 2 beta-stereochemistry, intramolecular cyclopropanation of the Delta(1(10)) bond by a 4 alpha-diazoacetyl group followed by Li-NH3 reduction, and then oxidative cleavage of the resulting cyclopentanone by oxygenation of the derived potassium enolate.