ChemInform Abstract: Crystallographic Evidence of [1,5]Prototropic Shifts Occurring Upon Transannular Diels-Alder Reaction of a 14-Membered Macrocycle Leading to a 5α-Steroid Skeleton

Reversible prototropic shifts from a stable 14-membered ring macrocycle (4Z, 10E, 12Z) - [1R * , 14S*]-1,8,8-tris-(methoxycarbonyl)-5-methyl-3,17-dioxobicydo[12.3.0]-heptadeca-4,10,12-triene, C 24 H 30 O 8 , occurred when the compound was heated to form rac-(5Z,11Z,13Z)-1,8,8-tris(methoxycarbonyl)-5-methyl-3,l7-dioxobicyclo-[12.3.0]heptadeca-5,11,13-triene, C 24 H 30 O 8 . The resulting compound crystallizes in a highly disordered fashion. After a transannular Diels-Alder reaction, the resulting adduct rac-3,3-bis(methoxycarbonyl)-18-oxo-5α,9β-androst-6-en-11,17-dione, C 24 H 30 O 8 , was then easily converted to a 5α-steroid core, rac-3,3-bis-(methoxycarbonyl)-18-oxο-5α-androst-6-en-11,17-dione, C 24 H 30 O 8 . The final adduct is an highly advanced intermediate for the total synthesis of naturally occurring aldosterone.