Cyclopentanes, -lactone-fused

The inexpensive, commercially available D-g/ycero-D-gw/o-heptono-1,4-lactone ( glucoheptonolactone since it is prepared from D-glucose) is the precursor for the 2,7-dibromo-2,7-dideoxy-D-g/ycm -D-/afo-heptono-1,4-lactone (1) (Scheme 13) which, via the unsaturated lactone 2a and radical induced carbocyclisation, could be transformed into the crystalline dihydroxy cyclopentane lactone 4a in high yield (Scheme 14). This short and efficient synthesis of the cis-fused cyclopentane lactone provides easy access to a chiral synthon which might be modified stereospecifically for many purposes. Such... 

Our approach was to use the unsaturated bromodeoxylactones in an intramolecular radical reaction, since these compounds possess both the radical precursor and the radical trap within the same molecule. Thus, reacting the unsaturated bromodeoxyheptonolactone 20 (Scheme 14) with tributyltin hydride and a radical initiator, the bicyclic lactone 65 a was obtained in a quantitative yield within 1 h. The stereocontrol in the reaction was determined by the structure of the product, since the compound obtained has two fused cyclopentane rings which can only be cis anellated. The radical A, which is the intermediate, was trapped by the tin hydride. The stereochemistry of the newly formed chiral center is determined by the configuration at C-4 in the educt 20 [45]. 

In an early step in an enantioselective total synthesis of certain prostaglandins <88T4989,92T10345>, application of the Prins reaction conditions to an unsaturated bicyclic lactone or ether (Equation (11)) afforded tricyclic heterocycles (31) containing cyclopentane-fused tetrahydrofuran and 1,3-dioxane units in 4-10% yield. The major products in each case were bicyclic diacetate derivatives of the starting material. 

The marine alga Laurencia hybrida produces a compound that has been isolated and characterized as hybridalactone (73). Structurally, this compound contains a 13-membered lactone ring fused to a cyclopentane ring. The macrocyclic ring, in addition to containing two (Z)-olefins, has a substituted cyclopropane ring appended ct to the lactone oxygen. 

In 2006, Nair disclosed the synthesis of ( )-tra s-l,3,4-trisubstituted cyclopentenes resulting from the addition of enals to chalcones catalysed by an achiral carbene." " Mechanistically, the addition of the generated homo-enol to enones to give adduct II, followed by intramolecular acylation to afford cyclopentane-fused p-lactone IV. The final cyclopentene 67 was formed by the in situ decarboxylation of the p-lactones (Scheme 20.32). The enantioselective variant of the process to access ds-cyclopentenes was reported by Bode et al. in 2007. ... 

D-Glucose has been converted to the bicyclic lactone 71, in which a key 3-carbon chain homologation is effected via aldehyde allylation. This lactone is a known precursor of acdnobolin, and this synthesis thus constitutes a formal total synthesis. ° The cyclopentane-fused 5-lactone 72, a potential prostaglandin synthetic intermediate, has been prepared from levoglucosan.3t... 

---