C_sp³–C_sp³ and C_sp³–H Bond Activation of 1,1-Disubstituted Cyclopentane

Abstract

The unprecedented C(sp(3))-C(sp(3)) bond cleavage of unactivated cyclopentane has been achieved. Rh(I)-catalyzed cycloaddition of allenylcyclopentane-alkynes produced in situ the 9-cyclopentyl-8-rhodabicyclo[4.3.0]nona-1,6-diene intermediates, which subsequently underwent [7+2] cycloaddition via β-C elimination, affording bicyclo[7.4.0]tridecatriene derivatives in good yields. Changing the Rh(I) catalyst effected the Cγ-H bond activation of the common 9-cyclopentyl-8-rhodabicyclo[4.3.0]nona-1,6-diene intermediate to produce the novel spiro[2.4]heptane skeleton in a site-selective manner.

Rh^I-Catalyzed Cycloaddition between Allenyl π-Bonds and C-C Triple Bonds

“…The reaction is initiated by the formation of the rhodabicyclic intermediate I. 12,13,16 There might be two possible pathways for the following insertion process of the external alkyne 39. One is insertion into the C sp2 Rh bond leading to the two intermediates V and V and the other is insertion into the C sp3 Rh bond resulting in formation of the two other intermediates III and III .…”

“…1, n 2). 13 This novel reaction involved unprecedented cleavage of the normal sized cyclopentane which has signi cantly lower strain energy (6.3 kcal/mol, Figure 2). 11 This chemistry was extended to a novel and unique C H activation; cycloisomerization of benzylallene terminal alkynes via cleavage of a C H bond on the benzene ring afforded 6/7/6 tricyclic ring systems (eq.…”

Construction of Azabicyclo[6.4.0]dodecatrienes Based on Rhodium(I)-Catalyzed Intramolecular [6+2] Cycloaddition between Azetidine, Allene, and Alkynes

“…9) This novel [7+2] cycloaddition involves the unprecedented cleavage of the normal-sized cyclopentane ring by releasing its strain energy (6.3 kcal/mol) 11) via the intermediate 3 (n=2), 8,9) similar to that of the cyclobutane derivatives.…”

“…Reductive elimination would occur to provide the final products. The successful application of this methodology to the cyclopentane derivative 1 (n=2) afforded the ninemembered bicyclic compounds 2 (n=2).9) This novel [7+2] cycloaddition involves the unprecedented cleavage of the normal-sized cyclopentane ring by releasing its strain energy (6.3 kcal/mol) 11) via the intermediate 3 (n=2), 8,9) similar to that of the cyclobutane derivatives.We now report the application of a newly developed eightmembered ring formation method for the preparation of the bicyclic azocine derivatives as well as the oxa analogue (Chart 2). The polycyclic skeleton containing an eight-membered heterocycle has been found as the core structure in various natural products and biologically-active compounds.…”

“…The unfunctionalized simple cyclobutane ring is generally known not to open, let alone being used as a C 4 -building block. [1][2][3][4][5] We tentatively interpreted that the production of 2 (n=1) would initiate the formation of the rhodabicyclo[4.3.0] intermediate 3 (n=1), [8][9][10] which should be susceptible to β-carbon elimination, [1][2][3][4][5] with release of the ring strain energy (26.3 kcal/mol) 11) giving rise to the nine-membered rhodabicyclic species 4. Reductive elimination would occur to provide the final products.…”