First Synthesis of Enantiomerically Pure Primary Helical Spirocycles Based on the Repetitive Addition of Lithiated Methoxyallene to Chiral 3(2H)‐Dihydrofuranone Derivatives

Repetitive additions to chiral 3(2H)‐Dihydrofuranones opened a route to the first enantiomerically pure primary helical spirocyclic compounds. Thus, addition of lithiated methoxyallene 2 to furanone 9 provided adduct 10 with excellent diastereoselectivity. Cyclization with potassium tert‐butoxide in DMSO followed by acid hydrolysis of the resulting enol ether moiety gave spirocyclic furanone 12 in very good overall yield. Repetition of this three‐step sequence converted 12 into 15. For the next series of reactions cerium compound 16 instead of 2 was employed as nucleophile which resulted in reasonable conversion of 15 into adduct 17. By application of the usual methods this compound was transformed into the enantiomerically pure tetracyclic spiro compound 19 in moderate overall yield. Functionalized spiro compounds as described in this paper may serve as enantiomerically pure building blocks in supramolecular chemistry.