No abstract

Different chiral spiroketal skeletons are obtained, in a versatile manner, by iterative alkylations of acetone N,N-dimethylhydrazone with iodides 2 followed by a one-pot deprotection/spirocyclization sequence. This methodology has been applied successfully to the synthesis of 1,7-dioxaspiro[5.5]undecane and 1,6-dioxaspiro[4.5]decane system

Epoxide 23. Compound 22 (150 mg, 0.55 mmol) was dissolved in dichloromethane (5 mL) and cooled (ice bath). m-Chloroperbenzoic acid (150 mg, 0.65 mmol, 70%) was added and the mixture was left (ice bath) for 12 h and then chromatographed (A1203, CH2C12/EtOAc 1:l) to give 23 [oil, 68 mg, 43%; ala^ + 6 4 O

The 1‐oxa‐7‐azaspiro[5.5]undecane, 1‐oxa‐6‐azaspiro[4.5]decane, 1‐oxa‐7‐azaspiro[5.4]decane and 1‐oxa‐6‐azaspiro[4.4]nonane ring systems are found as the cores of natural or synthetic products that possess significant biological activities. Because of their potential applications, together with the novelty of their skeletons, these compounds represent challenging targets for chemical synthesis. In this review we summarize the different strategies developed for the synthesis of these spiroaminals.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)