Pyrrolizidine from epoxides

A novel synthesis of (+)-mtegerrinecic acid lactone, the necic acid component of the macrolactone pyrrolizidine alkaloid integerrimine 53, has been reported by White and Jayasinghe, wherein lactonization of a 6-hydroxy acid was used for the ring closure [46] (Scheme 9). Reduction of epoxide 49 derived from / -(+)-P-citronellol and subsequent protection gave bis-3,5-DNB ester 50. Oxidative cleavage of the double bond afforded the carboxylic acid which upon saponification of the esters and acidification resulted in spontaneous lactonization to provide lactone 52. 

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