Naturally Occurring Fused Cyclopentanoids

Naturally Occurring Fused Cyclopentanoids.- An exceptional review on 

The arene-olefin cycloaddition reaction has now been applied to 

The regiospecific alkylation of tropylium iron tricarbonyl salts 

The ploy of ring expanding a stereospecifically formed cyclobutane to a cyclopentanone has been put to good use in a preparation of ( )-bakkenolide-A,in an enantioconvergent synthesis of 

Naturally Occurring Fused Cyclopentanoids.—Activity in this area continues to be intense. Little etal7 have used the rather low-yielding intramolecular 1,3-diyl trapping procedure in syntheses of A -capnellene (105) and the isomeric hirsutene (106), whereas in an alternative route to (105), sequential Nazarov and aldol cyclizations are used to build up the three ring system. Pyrolysis of the cage compound (107), derived from cyclopentadiene and 2,5-dimethylbenzo-quinone, leads to the hirsutene precursor (108) in high yield. The preparation of another potential precursor (110) to the hirsutanes by intramolecular [2 2]photoaddition of (109) has been detailed in full.  

Danishefsky et aC have presented in full their syntheses of ( )-coriolin (111) and ( )-coriolin-B, which feature the cyclopentenone-annulation procedure (112) - (113) at the outset. Japanese workers have also achieved total syntheses of ( )-coriolin in which one key step is the conversion of 1,3-cyclo-oc- 

Yamazaki, M. Shibasaki, and S. Ikegami, Tetrahedron, 1981, 37, 4411 K. Tatsuta, K. Akimoto, and M. Kinoshita, ibid., p. 4365 see also M. Yamazaki, M. Shibasaki, and S. Ikegami, Chem. Lett., 1981, 1245. 

New methods for the elaboration of the gibbane carbon skeleton and related Structures continue to be developed. Chiral gibbane derivatives can be prepared by asymmetric aldol condensations using L-proline as catalyst, or by building up the carbon skeleton from a chiral precursor. Examples have already been quoted which bear witness to the considerable synthetic potential of acid-catalysed intramolecular cyclizations of olehnic diazoketones. Mander etal. have given full details of their studies in this area with anisole derivatives such as 

Biichi s approach to bicyclo[3.2.1]octanes based on the acid-catalysed or photochemical addition of p-quinone monoacetals to olefins has been used in a 

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