Cyclopentane stereospecific synthesis

Stereospecific carbocyclisation formation of a bicyclic cyclopentane-lactone. Synthesis of carbahexofuranoses... 

Stereospecific synthesis of arylidene and allylidene cyclopentanes and cyclohexanes can be achieved by palladium-catalyzed cyclization of carbanions containing a C — C triple bond in the presence of aryl or vinyl halides52 33". The reaction is stereoselective, occurring with irans selectivity. Thus, a palladacyclic intermediate, resulting from initial aryl or vinyl carbapallada-tion, is ruled out in favor of primary carbanion addition to the alkyne unit. 

One early example was reported by Chatteijee in 1979 for stereospecific synthesis of the sesquiterpene isocomene by transannular cationic cyclization. The acid-catalyzed cyclization of epoxide 152 through transannular participation of the remote double bond led to the formation of 153 (Scheme 20.37), which was further transformed to isocomene. The reaction was stereoselective since formation of any other diastereomers will lead to the formation of much strained polycyclic systems with trans-fased cyclopentanes. 

In the Woodward synthesis of prostaglandin (621, intermediate 172 formed in situ from the corresponding amine was smoothly transformed into bicyclic aldehyde 173. Seebach and co-workers (63) have also observed several stereospecific rearrangements using the same reaction. For example, diazotization of amine 174 gave specifically the cis-cyclopentane 175 which was then epimerized into the more stable trans-cyclopentane 176. 

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... 

A new synthesis of chiral cyclopentanoid intermediates involves the stereospecific reaction of the carbanion (30) with the tartaric acid derived epoxide (31). An intramolecular enolate anion alkylation, induced by a Michael reaction, has been utilized in the preparation of cyclopentanes (Scheme 6). Additionally, variation... 

Practicable syntheses of four-, five, and six-membered carbocyclic rings have been achieved by reaction of a,to-di-Grignard reagents with silver(i) salts. Conversion of l,3-bis(chloromethyl)cyclopentane into norbornane was effected in 82% yield, but was the only bridged-ring synthesis reported. Stereospecific cyclic ketone formation using iron(O) compounds has been reviewed. ... 

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