Synthesis of Aromatic Spiroacetals

Abstract

The synthesis of aromatic spiroacetal ring systems related to the papulacandins is reported. ortho-Metalation of diisopropylbenzamide, followed by reaction with the electrophiles δ- valerolactone, γ- butyrolactone and γ-valerolactone, provided the keto alcohol adducts (10),(16) and (21) respectively. Reduction of the ketone followed by treatment with acid afforded phthalides (12),(18) and (23). Finally oxidative cyclization with iodobenzene diacetate provided the spiroacetals (7),(14) and (19).

Total Synthesis of Cryptoacetalide

“…On the basis of the model studies shown in Table , the [2+2+2] cyclotrimerization reaction was conducted with Cp*RuCl(COD) in toluene under microwave irradiation (300 W) affording the tricyclic product 23 in 90% yield. Deprotection of the PMB ether with DDQ generated the corresponding alcohol 24 , which set the stage for the spiroketalization reaction . The lacton 24 was irradiated with light (200 W Xe/Hg lamp) in the presence of iodine and iodobenzene diacetate for 1 h. The natural products cryptoacetalide ( 1 ) and epi -cryptoacetalide ( epi - 1 ) were isolated as a 2:1 mixture in an excellent yield of 84% (Scheme ).…”