Cycloalkenyl

Starting with 2-ethynylaniline, Cacchi and co-workers have prepared 2-aryl and 2-(cycloalkenyl)indoles by coupling followed by cyelization[7]. The reagents for the coupling step are Pd(PPh3)3. Cul Et2NH. The cyclization is... 

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. 

Symmetrical labile ethers such as cycloalkenyl ethers (15) or mixed acetals (16) can also be prepared from the 3-hydroxyl group by acid-catalyzed exchange etherification or by acid-catalyzed addition to cyclohexanone methyl enol ether. 

Beta- and 3a-alcohols of the 5)5- and 5a-series respectively also form tetrahydropyranyl ethers, cycloalkenyl ethers and mixed acetals. ... 

Application of this scheme to condensation products of cyclo-alkanones affords the cycloalkenyl-substituted barbiturates. 

The metathesis of acyclic alkenes substituted with other hydrocarbon groups, such as cycloalkyl, cycloalkenyl, or aryl groups, has also been observed. For instance, styrene is converted into ethene and 1,2-diphenyl-ethene (stilbene) (9, 9a). 

Cycloalkenyl sulphones, reactions of 646 Cycloalkyl aryl sulphones, lithiated 641 Cyclodextrins 59, 72 in asymmetric synthesis of sulphoxides 292... 

Bis(4-hydroxyphenyl) sulphones butadienyl - see Butadienyl sulphones chiral - see Chiral sulphones complexes of 573 cyclic - see Cyclic sulphones cycloalkenyl - see Cycloalkenyl sulphones cycloalkyl aryl - see Cycloalkyl aryl sulphones... 

Table 31 Synthesis of compounds TsRs where R is a cycloalkyl, cycloalkenyl, or substituted aryl group... 

An allylic sulfenate, like 199, is known to be in equilibrium with allylic sulfoxide, like 196, although its concentration is usually low . Various allylic sulfoxides can be prepared by treatment of allylic alcohols with arenesulfenyl chlorides . Evans and coworkers prepared various allylic alcohols by treating the corresponding allylic sulfoxides with trimethyl phosphite. For example, the carbanion from a cycloalkenyl sulfoxide 201 was readily alkylated at the a-position by treatment with alkyl halide. The resulting alkylated derivative 202 was then treated with trimethyl phosphite and 3-substituted cycloalkenol was obtained. Alkylation of acyclic allylic sulfoxide 204 gave... 

Scheme 1.11 Mixed S / P ligands for Pd-catalysed allylic substitutions of cycloalkenyl acetates.

Using 3-Bromocycloalkyl Hydroperoxides obtained by Bromination of 2-Cycloalkenyl Hydroperoxides... 

Peroxide ring closures were effected by stirring the 2,3-dibromocycloalkyl hydroperoxides with silver trifluoroacetate, and the bromo-substituted bicyclic peroxides were isolated by silica chromatography at —25 °C. Yields (based on 2-cycloalkenyl hydroperoxide) of 56 and 38% were achieved respectively for the [3.2.1]- and [4.2.11-compounds, but only 16% of the [2.2.1]- and 13% of the [5.2.1]-peroxide was obtained. The main reason for the low yield of the [2.2.1]-peroxide was that substitution by trifluoroacetate, which competes with the desired dioxabicyclization, is particularly prevalent with the 5-membered ring. 

A combination of cyclizations and a cycloaddition was observed by Aumann and coworkers [308] by reaction of a cycloalkenyl-ethynyl tungsten-carbene 6/4-109 with an alcohol to give 6/4-112 (Scheme 6/4.27). The last step in the sequence is a jt-cyclization with insertion of CO of the intermediate cycloadduct 6/4-111 formed from 6/4-110 and 6/4-109. 

The resultant cycloalkenyl carbenium ions, especially the cyclopentenyl cations, are very stable (103,104) and can even be observed as free cations in zeolites 105,106). These ions can oligomerize further and, within zeolites, irreversibly block the acidic hydroxyl groups. With liquid acids, the oligomers will dilute the acid and thus lower its acid strength. 

Intramolecular Heck reactions.6 Heck intramolecular coupling of alkenyl or aryl iodides substituted by 3-cycloalkenyl group is an attractive route to fused, spiro, and bridged polycyclic products. Coupling is achieved with a Pd-phosphine catalyst such as Pd[P(QH5),]4 in combination with a base, N(C2H5)3 or NaOAc. The coupling tends to produce a mixture of two isomeric alkenes, in which the newly formed bond is allylic or homoallylic to the ring juncture. 

Cyclic alcohols exhibit the simplest behaviour. Cyclic aliphatic alcohols and olefins immediately form alkyl cations which can abstract hydride from their equilibrium olefins giving the corresponding hydrocarbon and the corresponding cycloalkenyl cation (equations 11 and 12). 

Table 2 Nonprotein amino acids containing alkenyl, cycloalkenyl, or alkynyl side chains...

Studied by Olah (Olah and Liang, 1972 and Olah et al., 1972a) were chosen—the methyl substituted cycloalkenyl cations, represented hy solid dots, and the substituted aryldimethylcarbonium ions, represented by open circles. The correlation to a line of slope 0 0146 is excellent for all but two of the points. If the Spiesecke-Schneider value of 160 p.p.m. is used for the linear charge dependence of the carbon-13 shifts, then the calculated value for the methyl shifts is... 

Usually, the enantiomeric ratios decrease on prolonged reaction times to approach the thermodynamically determined ratios of diastereomers. Notable exceptions are the lithium-)—)-sparteine derivatives of (2-methyl-l-cycloalkenyl)methyl carbamates ewf-303d... 

Kinetic resolution (enantiomer differentiation) of cycloalkenyl diazoacetates has been achieved (for example, according to Eq. 3) [34]. In these cases one enantiomer of the racemic reactant matches with the catalyst configuration to produce the intramolecular cyclopropanation product in high enantiomeric excess, whereas the mismatched enantiomer preferentially undergoes hydride abstraction from the allylic position [35] to yield the corresponding cycloalkenone. With acyclic secondary allylic diazoacetates the hydride abstraction pathway is relatively unimportant, and diastereoselection becomes the means for enantiomer differentiation [31]. 

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