Cyclopent annelation

Heating of the 2-(allenyl)phenyl azides 79 at 110 °C gave a mixture of the cyclopent-annelated indoles 80 and 81 °. ... 

Cyclopent-2-enone rings can be easily obtained under mild conditions from a,a-dibromoketones and enamines in the presence of iron carbonyls Spiro-annelation with S-cyclopropylids provides easy access to spiropentane derivatives and similar compounds . Ring expansion from 5- to 7-membered rings has been efficiently performed with cyclopropenes The transformation of nerolidol to the tricyclic a-cedrene has been achieved by a remarkable stepwise cyclization process... 

Boron fluoride I hydrogen chloride Cyclopent-2-enone annelation... 

Numerous new examples of annelation reactions involving alkyne-hexacar-bonylcobalt complexes and norbornene derivatives have been reported it seems that the alkyne and alkene units are joined at the less hindered position of each, subsequent addition of the carbonyl group leading to the observed cyclopent-2-enone derivatives. A new synthesis of tetrasubstituted cyclopent-2-enones (39) by cyclocarbonylation using tetracarbonylnickel has been presented. 

General Methods.—Trost and his co-workers have extended their earlier studies of the synthesis of cyclopentanes based on thermolysis of vinylcyclopropanes, and shown that it is expedient to use the recently developed 1-lithiocyclopropyl phenyl sulphide (32) for the preparation of the appropriate vinylcyclopropane precursor. Thus addition of (32) to ketone (33), followed by dehydration of the intermediate hydroxy-sulphide with SOCI2, led to (34), which on thermolysis in the vapour phase at 350 °C, then hydrolysis, gave the cyclopentenone (35). An identical approach to cyclopentane annelation has been used by Miller in a synthesis of (36) from cyclopent-2-enone. 

---