Cyclopentane annelation

H. Hashimoto, K. Furuichi, and T. Miwa, Cyclopentane annelated pyranosides A new approach to chiral iridoid synthesis, J. Chem. Soc. Chem. Commun. p. 1002 (1987). 

Intramolecular conjugate allylation (12, 25).2 Fluoride ion catalyzes intramolecular Michael additions of allyltrimethylsilane to a,p-enones as well as a,p-unsaturated esters, nitriles, and amides Lewis acid catalysis is not effective. The method is particularly suited to cyclopentane annelations.2... 

Cyclopentane annelation.1 A recent synthesis of the sesquiterpene silphinene (7) used two cyclopentane annelations, both involving conjugate addition of the Grignard reagent derived from 1 in the presence of CuBr S(CH3)2 to an a,/ -enone. Thus 3, obtained as shown, undergoes dehydration to 4. This product was converted to 5, which undergoes a second cyclopentane annelation to give eventually 6, which has the carbon skeleton of 7. 

A cyclopentane annelation by intramolecular C—H insertion of intermediate cationic iron-carbene complexes has been applied to the synthesis of the fungal metabolite ( )-sterpurene [49]. 

Crandall, J. K. Magaha, H. S. Magnesium-induced cyclizations of 2-(3-iodopropyl)cyclo-alkanones. A cyclopentane annelation method. J. Org. Chem. 1982, 47, 5368-5371. 

Cyclopentane anndation. Trost and Keeley have described a new method for cyclopentane annelation (equation I). Yields are high in all steps, and the... 

CYCLOPENTANE ANNELATION Lithium phenylthio(cyclopropyl)cuprate. 

Cyclopentadienyllithium, 239 Cyclopentadienyltitanium trichloride, 374 Cyclopentane annelation, 190, 211-212 Cyclopentenones, 24, 253, 278 Cyclopentylidenetriphenylphosphorane, 183... 

Cyclopentane annelation. This cuprate reacts with j3-halo-a, -unsaturated ketones to form J-cyclopropylenoncs. The products rearrange on thermolysis to cyclopcnlanc systems. An example of this annelation method is formulated in equation (I). 

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. 

In extensions of some earlier studies, Wada et al. have shown that a useful method of cyclopentane annelation is by rearrangement of protonated cyclopropyl ketones, to y-hydroxy-ketones, viz. (51), followed by oxidation to 1,4-diones and base-catalysed cyclization (Scheme 16). Both oxidation of a-allyl-ketones, using PdCl2-CuCl in DMF under an oxygen atmosphere, and the oxidative cleavage of t-cyclobutanols using Jones reagent provide alternative new approaches to... 

---