Alkene from cycloalkene

From studies of the telomerization between 1-alkenes and cycloalkenes another interesting result emerged. The expected triads were observed, but within each triad the ratio of the products varied between 1 10 1 and 1 20 1 (88). This is not consistent with the scheme of H6risson and Chauvin. However, with the scheme of Calderon, this can be explained if... 

For the cleavage of alkenes from a support by metathesis, several strategies can be envisaged. In most of the examples reported to date, ring-closing metathesis of resin-bound dienes has been used to release either a cycloalkene or an acyclic alkene into solution (Figure 3.38, Table 3.44). Further metathesis of the products in solution occurs only to a small extent when the initially released products are internal alkenes, because these normally react more slowly with the catalytically active carbene complex than terminal alkenes. If, however, terminal alkenes are to be prepared, selfmetathesis of the product (to yield ethene and a symmetrically disubstituted ethene) is likely to become a serious side reaction. This side reaction can be suppressed by conducting the metathesis reaction in the presence of ethene [782,783]. 

Transfer of carbene 3a from 19 to a variety of alkenes and cycloalkenes has been achieved under catalysis by copper(I) chloride74,79 - 82. However, with the exception of cyclohexene69,70 (72% yield), only moderate yields could be obtained. In all cases, the cyclopropanation was stereospecific with respect to the double bond configuration of the alkene and gave the sterically less crowded cyclopropane diastereomer in excess. As in the photochemical cyclopropanation, the formal carbene dimer trans-1,2-bis(trimethylsilyl)ethene is often formed as the major by-product. Cyclopropanation of fraws-but-2-ene with 19 with copper(II) chloride as catalyst was found to be even less... 

Sodium amalgam is effective for promoting defluorination (Scheme 14), to produce an interesting series of dienes (38), (40) and (42), especially (38) [7, 8, 36], but tetrakis(dimethylamino)ethene (TDAE) (43) (Scheme 15) is a much safer system to use and, consequently, with the latter reagent, the process may be scaled up [36]. TDAE (43) is successful because its donor capacity is high, i.e. it has been variously described as being similar to that of zinc [37] or to alkali-metals [38] and will react, therefore, with most perfluorinated alkenes or -cycloalkenes. Furthermore, the fact that the dienes (38), (40) and (42) may be isolated derives from the fact that the dienes have more CF= sites than the starting alkenes and consequently their respective reduction potentials vary by... 

Various oligomers of fluorinated alkenes and cycloalkenes have been prepared by fluoride ion induced oligomerisation of various monomers (Sect. 5.3), and the chemistry of these systems provides some unique reactions. The oligomers of special interest here may be described as of types (95) or (96) (Scheme 59), i. e. systems with either four (95) or three (96) perfluoro-alkyl or -cycloalkyl groups attached to the double bond, whereas systems with two perfluoroalkyl groups attached, i. e. (97) and (98), have a chemistry more similar to fluorinated alkenes that may be derived from other sources. 

TABLE 4.9 Alkene and Cycloalkene Chemical Shift (ppm from TMS)... 

There is no need to isolate this compound in order to effect addition of diphenyl disulphide (and dimethyl disulphide) to alkenes in this way tran. -l,2-bis-phe-nylthio (and methylthio) adducts were formed from cycloalkenes and 1-hexene. 

Pseudonitrosites and a-nitro ketone oximes were identified as intermediates in this process. This route has since been developed to provide access to mono- and poly-cyclic furoxans from readily-available alkenes and cycloalkenes. Treatment of the alkene with dinitrogen trioxide affords the nitro-nitroso adduct, which is readily isolated as its nitroso dimer (pseudonitrosite) thermal isomerization to the a-nitro ketone oxime, followed by dehydration with cyclization leads to the furoxan (Scheme 19). 

Acid-catalyzed epoxide cleavage takes place by back-aide attack nucleophile on the protonated toxide in a manner analogous to the step of alkene bromtnation, in ndiich a cyclic brentORtunt ion is opened nucleophilic attack (Section 7.2l. When an opoxycycloalkane is opened aqueous acid, a frona-t -diol results just as a traR5 l,2-dibroiiiide from cycloalkene hrominaUun. 

Heating alkenes and cycloalkenes with manganese triacetate yields lactones resulting from an oxidative addition of acetoxyls across the double bonds (equation 88) [50J]. 

OL-Jodo ketones result from the reaction of alkenes and cycloalkenes, especially the electron-rich ones, with silver chromate and iodine (equations 92 and 93) [<5i6]. 

Acid-catalyzed epoxide cleavage takes place by back-side attack of] nucleophile on the protonated epoxide in a manner analogous to the fn step of alkene bromination, in which a cyclic bromonium ion is opened 1 nucleophilic attack (Section 7.2). When an epoxycycloalkane is opened 1 aqueous acid, a rans-1,2-diol results, just as a from cycloalkene bromination. 

Mechanisms of hydrolysis of epoxides derived from simple alkenes and cycloalkenes 250... 

Olefins - Acyclic and cyclic hydrocarbons having one or more carbon-carbon double bonds, apart from the formal ones in aromatic compounds. The class olefins subsumes alkenes and cycloalkenes and the corresponding polyenes. [5]... 

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