1-Cyclopentenecarboxylic acid

S-Brum<)cyclo1aiexan carboxylic acid I -Cyclopentenecarboxylic acid... 

Photocycloaddition of chiral esters of cyclohexenone-3-carboxylic acid 168 or of cyclopentenecarboxylic acid 175 led to mixtures of stereoisomeric cycloadducts with variable diastereoselection, as shown in Scheme 28 [148]. 

Protonated pyridines can also be used as acceptors of carbon radicals generated from thiohydroxamates in general. A useful extension of the Michael addition reacations is to incorporate an additional t-butylthio substituent into the acceptor component (eq 16). Tandem reactions are also possible, as exemplified by the conversion of a cyclopentenecarboxylic acid into a bicy-clo[2.2.1]heptane (eq 17). ... 

The readily available methyl 3,3-dimethylcyclopropene-l-carboxylate (III/54) undergoes [2+2] cycloaddition with enamines e.g. the morpholine derivative III/55 to give 2-aminobicyclo[2.1.0]pentane derivatives, e.g. III/56. These compounds are transformed into cyclopentane derivatives, e.g. methyl 4-hydroxy-2,5,5-trimethyl-1-cyclopentenecarboxylate (III/57) by treatment with dilute mineral acids. 

An improved method for the preparation of methyl 2-oxo-5-vinyl-cyclopen-tanecarboxylate (389) by treatment of dimethyl ( )-2-hexenedioate (390), with the cuprate made from vinyllithium and copper(I) cyanide (77-85%), led to a short synthesis of mitsugashiwalactone (391) (Scheme 34), another noriridoid isolated from Boschniaka rossica Borohydride reduction and dehydration gave methyl 5-vinyl-l-cyclopentenecarboxylate (392), and this could be cyclized by hydroboration and extended treatment with hydrogen peroxide—conditions for the highest yield in the cyclization seem to be with hydroboration in base— then a separate acid-catalyzed cyclization. The methyl group was added with lithium dimethyl cuprate. ... 

Addition of chiral lithium (5)-(a-methylbenzyl)benzylamide to tert-butyl 1-cyclopentenecarboxylate (77) at -95 °C, followed by quenching with 2,6-di-ter/-butylphenol, gave 78 in 98% diastereomeric excess. 78 was debenzylated catalytically and, after acidic hydrolysis and desalting on Dowex resin, afforded pure cispentacin 5 (Scheme 12) [94]. 

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