Cyclopentane annulation

Reaction of the imine moiety of 278 with excess ethyl diazoacetate in the presence of Cu(acac)2 led to the cyclopentane-annulated product 279 the structure of which was confirmed by an X-ray analysis 262. It is assumed that 279 results from reaction between a carbene dimer (diethyl fumarate) and an intermediate N-ylide or the... 

The reaction pathway may be supported by the observations with 4,4-dimethyl-5-trimethylsilyloxyhept-l-en-6-yne and its positional isomer 4,4-dimethyl-3-trimethylsilyloxyhept-l-en-6-yne. These react with Me2PhSiH to give the corresponding aldehydes, 280 and 282, respectively, as a mixture of two diastereomers under the conditions similar to mode 1 in Scheme 13 (Equations (47) and (48)). In the reaction of 281, an appreciable amount of 283 is formed concomitantly, which implies that the trimethylsilyloxy group at an allylic position likely retards the cyclopentane annulation step. 

I. Marco-Contelles and J. Ruiz-Caro, Iridoids from carbohydrates via Pauson-Khand reaction synthesis of advanced highly oxygenated cyclopentane-annulated pyranosides from D-glucal derivatives,. /. Org. Chem., 64 (1999) 8302-8310. 

I(Cyclopentadienyl)dicarboayM phate, Cp(CO)2Fe+=CHSC H, phenylthio iron carbene is obttii C1CH2SC6H3 and then with (C H Cyclopentane annulation.2 by insertion into C-H bonds. Thi... 

Cyclopentane annulation.2 This complex is useful for cyclopentane annulation by insertion into C-H bonds. Thus reaction of 1 with the enolate of ketone 2 provides... 

Fig. 1.42. Cyclization of a 5-hexenyl radical intermediate from a Barton-McCombie defunctionalization as a method for cyclopentane annulation (cyclizing defunctionalization, in terms of Figure 1.2 this means a "substitution including a fragmentation and an addition ).

Similar cyclopentane annulations of allylsilanes with benzotropylium salts149,150, tetracyanoethylene151, benzyl cations152 and l,2,4-triazoline-3,5-diones had been reported153. 

Fig. 1.35. Cyclization of a 5-hexenyl radical intermediate from a Barton-McCombie defunctionalization as a method for cyclopentane annulation.

An entry to cyclopentane-annulated ni from 4-nitroalkyl-3-allylthiolactams <03s/ natural products, is substituent at C-6 if either the 2-nitropropyl group ... 

Cyclic p-kcio esters and )9-diketones (596) smoothly effect ring-opening of 1,1-bis(benzenesulphonyl)cyclopropane (412) under basic conditions. Reductive cleavage of the resulting sulphones (597) by lithium arylides provides routes to 598 and 599 (equation 210) The bis-benzenesulphonyl compound appears to fulfil the requirements for a propylene 1,3-dipole. The fact that the sulphones can be sequentially removed permits selective introduction of from one to three electrophiles (E) (equation 211). In the case of )5-keto esters, such versatility created a novel three carbon insertion between the ester group and the ketone or a cyclopentane annulation. ... 

The process has also been extended to the X = C series. The ring expansion-cyclopentane annulation provides good yields for the five- to six- (82%), six- to seven- (90%) and seven- to eight-membered ring (75%) ketone series studied (Scheme 74 equations 32 and 33). ... 

As shown in Scheme 60, treatment of chromones 299b-c with f-butyldi-methylsilyl triflate affords the 1-benzopyrylium triflates 45b-c. Reaction of 45b-c with 3-(trimethylsilyl)-l-butene gives the cyclopentane annulation products 49a (87%) and 49b (37%) along with a small amount of the allyla-tion product 48 from 299c (90CL1725 91JOC2058). 

However, there are still a number of problems that will have to be solved Synthetic equivalents will have to be found for those cosubstrates that do not undergo this cycloaddition. The possibilities of inversion the polarity (e.g. by the introduction of a nitro-group at the unsaturated cosubstrate) remain to be examined as does the extension of these cycloaddition reactions to an intramolecular version leading to cyclopentane annulation. Although the regioselectivity may be manipulated by changing the catalyst (e.g. Pd(0) versus Ni(0)), there is still room for improvement and a deeper understanding of the mechanistic details of these reactions is needed. But the activity and the interest in this field assure that most of these problems will be solved in the near future. 

In a similar manner, the corresponding cyclopentane annulated spirocyclobutanones 40 were obtained in high yield. Clearly, initial formation of a terminal oxonium ion which undergoes stereoselective addition to the vinyl bond induces the cyclopropylmethyl to cyclobutyl cationic rearrangement. 

Minami, T., Nakayama, M., Fujimoto, K., and Matsuo, S., A new approach to cyclopentane annulated compounds via l-(cyclopent-l-enylcarbonyl)vinylphosphonates, J. Chem. Soc., Chem. Commun., 190, 1992. 

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