Coupling cyclopentene

Sect. 2.1.1) and [3C+2S] cyclopentene derivatives. The product distribution can be controlled by choosing the appropriate reaction conditions [72]. Moreover, the cyclopentene derivatives are the exclusive products from the coupling of fi-pyrrolyl-substituted carbene complexes [72b,c] (Scheme 25). The crucial intermediate chromacyclobutane is formed in an initial step by a [2+2] cycloaddition. This chromacyclobutane rearranges to give the rf-complex when non-coordinating solvents are used. Finally, a reductive elimination leads to the formal [3C+2S] cyclopentene derivatives. 

Coupling of alkenylcarbene complexes and siloxy-substituted 1,3-dienes affords vinylcyclopentene derivatives through a formal [3C+2S] cycloaddition process. This unusual reaction is explained by an initial [4C+2S] cycloaddition of the electron-poor chromadiene system as the 471 component and the terminal double bond of the siloxydiene as the dienophile. The chromacyclohexene intermediate evolves by a reductive elimination of the metal fragment to generate the [3C+2S] cyclopentene derivatives [73] (Scheme 26). 

Cyclopentene, cyclohexene, and cycloheptene were obtained by intramolecular oxidative couplings of the bis-ylides (161 n = 3, 4, or 5) but oxidation of (161 n = 2) gave cyclo-octa-1,5-diene. Oxidation of the bis-ylide (161 n — 8) gave cyclic polyenes containing 20, 30, 40, 50, and 60 atoms. 

A total synthesis of the sesquiterpene ( )-illudin C 420 has been described. The tricyclic ring system of the natural product is readily quickly assembled from cyclopropane and cyclopentene precursors via a novel oxime dianion coupling reaction and a subsequent intramolecular nitrile oxide—olefin cycloaddition (463). 

Abstract The coupling of 2-azabicyclo[2.2.1]hept-5-en-3-one and trimethylsily-lacetylene or phei rlacetylene under Domino Heck conditions gives compounds 2a-c and 4a-c in moderate yields and cyclopentene derivatives, 3a-c in low yields. The procedure can be of use for the synthesis of alkynyl bicyclic lactams. 

Other derivatives were prepared by modifications of the original Ellman route. Thus, a second cyclopentene precursor 18 containing the C5 6 cis double bond was carried through to give the resin-bound intermediate 19 via a Stille coupling and an oxidation. Subsequent cuprate addition, reduction, and cleavage give 20 and 21 (the F and E series) with the C56 double bond intact. This type of approach was used to synthesize 11 more compounds in this series. 

The ruthenium-catalyzed addition of C-H bonds in aromatic ketones to olefins can be applied to a variety of ketones, for example acetophenones, naphthyl ketones, and heteroaromatic ketones. Representative examples are shown in the Table 1. Terminal olefins such as vinylsilanes, allylsilanes, styrenes, tert-butylethy-lene, and 1-hexene are applicable to this C-H/olefin coupling reaction. Some internal olefins, for example cyclopentene and norbornene are effective in this alkylation. The reaction of 2-acetonaphthone 1 provides the 1-alkylation product 2 selectively. Alkylations of heteroaromatic ketones such as acyl thiophenes 3, acyl furans, and acyl pyrroles proceed with high yields. In the reaction of di- and tri-substitued aromatic ketones such as 4, which have two different ortho positions, C-C bond formation occurs at the less congested ortho position. Interestingly, in the reaction of m-methoxy- and m-fluoroacetophenones C-C bond formation occurs at the congested ortho position (2 -position). 

Campbell, J.A. et al. Chirospecific Syntheses of Precursors of Cyclopentane and Cyclopentene Carbocyclic Nucleosides by [3+3]-Coupling and Transannular Alkylation. 2.4 1995(111]... 

This formation of (i-lactones is strongly related to a serendipitous finding made by Nair et al. (Nair et al. 2006b Chiang et al. 2007 Phillips et al. 2007). Interestingly, they found that the IMes-catalyzed coupling of a,P-unsaturated aldehydes with a,P-unsaturated ketones led to the stereoselective formation of Pms-substituted cyclopentenes... 

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