Intermediates of Prostanoid Synthesis. Stereospecific conversion of (+)‐5β‐hydroxycyclopenten‐2‐yl‐1β‐acetic acid γ‐lactone into (+)‐1β‐methoxycarbonylmethyl‐2β,3β‐(p‐nitrobenzylidene)‐dioxycyclopentan‐5‐one

Abstract

Starting from (+)‐5β‐hydroxycyclopenten‐2‐yl‐1β‐acetic acid γ‐lactone (1), (+)‐1β‐methoxycarbonylmethyl‐2β, 3β‐(p‐nitrobenzylidene)‐dioxycyclopentan‐5‐one (7) was prepared within 4 steps. Subsequent cleavage of the latter gives (−)‐3β‐hydroxy‐1‐methoxy‐carbonylmethylcyclopent‐1‐en‐5‐one (8a). Hydroxylation of the lactone (1) was found to give (+)‐2β,3β,5β‐trihydroxycyclopentyl‐1β‐acetic acid γ‐lactone (2a) with cis‐oriented hydroxy groups in respect to the lactone ring. No formation of the trans‐isomer, as has been reported earlier [4], was observed.

Origins of Stereoselectivities of Dihydroxylations of cis-Bicyclo[3.3.0]octenes

“…13–15 In example (i), dihydroxylation of cis -oxabicyclo[3.3.0]octenone 9 took place preferentially from the concave face to give the β-diol product 10 . In the first report of this transformation, 13a the major product was assigned—without experimental evidence—as arising from convex-face dihydroxylation, but this structural assignment was later reversed by means of an X-ray crystal structure. 13b In the second example (ii), cis -bicyclo[3.3.0]octenone 11 was dihydroxylated also preferentially from the concave face to give diol 12 with relatively low 4:1 selectivity.…”

“…In the first report of this transformation, 13a the major product was assigned—without experimental evidence—as arising from convex-face dihydroxylation, but this structural assignment was later reversed by means of an X-ray crystal structure. 13b In the second example (ii), cis -bicyclo[3.3.0]octenone 11 was dihydroxylated also preferentially from the concave face to give diol 12 with relatively low 4:1 selectivity. 14 It was hypothesized in this report that the selectivity may be due to a directing effect of the carbonyl group, as conversion of the ketone into a protected β-alcohol inverts the facial selectivity.…”

“…These are representative of the types of molecules included in the 26 examples in the Supporting Information. These do not include substituents, and comprise one cyclic ketone, 11 , and two lactones, 9 and 13 . − In example (i), dihydroxylation of cis -oxabicyclo[3.3.0]octenone 9 took place preferentially from the concave face to give the β-diol product 10 . In the first report of this transformation, the major product was assigned, without experimental evidence, as arising from convex-face dihydroxylation, but this structural assignment was later reversed by means of an X-ray crystal structure .…”