Aryl acyclic

Acyclic Enones as Substrates Compared to cyclic enones, acyclic enones are generally more challenging substrates for the copper-catalyzed asymmetric 1,4-addition reactions. Several ligands have been reported that can achieve high ee when p-aryl acyclic enones are used as substrates in the 1,4-addition of diethyl-zinc (Figure 3.5). ° ... 

Figure 3.5. Chiral hgands that exhibit >90% ee in the reaction between P-aryl acyclic enones and diethylzinc under copper catalysis.

The 6/Pd-catalyst system is very effective at the arylating acyclic secondary amines with aryl triflates in moderate to good yield, Eq. (62) [42 a]. 

In some cases, the acyclic intermediates (229) of 230, R] = aryl, R2 = hydrogen, were isolated (424), They undergo cyclization to thiazoles upon heating in toluene. Some 2-aryl-4-hydroxythiazoles prepared by this procedure are listed in Table 11-39. 

Aryl and a,/3-unsaturated 1830-1780 intense in acyclic anhydrides, and the lower-frequency band is more intense in cyclic anhydrides. 

Alkylisothiazolium salts (61) undergo N—S bond cleavage when treated with hydrogen sulfide or thiophenol to form acyclic products (62), but 2-aryl compounds give 1,2-dithioles (63 or 64 Scheme 9) (75SST(3)54l, 77SST(4)339). 

The procedure described is an example of a more general synthetic method for the direct conversion of ketones into cyanides. " The reaction has been carried out successfully with acyclic and cyclic aliphatic ketones, including numerous steroidal ketones and aryl-alkyl ketones. The conversion of diaryl or highly hindered ketones such as camphor and )3,j8-dimethyl-a-tetralone requires the use of a more polar solvent. The dimethoxyethane used in the present procedure should be replaced by dimethyl sulfoxide. ... 

The photocyclization of N-aryl enamines derived from cyclic or acyclic ketones proceeds under mild conditions to produce 2,3-dihydroindole derivatives (178b). The stereochemistry of the products is predominantly trans, which follows from a photochemical electrocyclic process which should take place in a conrotatory manner (178c,I78d). However, the presence of some cis products is not as easily explained. 

The reactions of enamines as 1,3-dipolarophiles provide the most extensive examples of applications to heterocyclic syntheses. Thus the addition of aryl azides to a large number of cyclic (596-598) and acyclic (599-602) enamines has led to aminotriazolines which could be converted to triazoles with acid. Particular attention has been given to the direction of azide addition (601,603). While the observed products suggest a transition state in which the development of charges gives greater directional control than steric factors, kinetic data and solvent effects (604-606) speak against zwitterionic intermediates and support the usual 1,3-dipolar addition mechanism. 

Organoboron reagents ate pariictdarly well suited for 1,4-additions of aryl and vinyl groups to enones. Hayasbi et al. developed a highly enantioselective RliQ)/ BlNAP-catalyzed 1,4-addilion of pbenylbotonic add lo cyclic and acyclic enones [24] fSclieme 7.5) and 1-alkenylpbospbonales [25]. 

The Pauson-Khand reaction was originally developed using strained cyclic alkenes, and gives good yields with such substrates. Alkenes with sterically demanding substituents and acyclic as well as unstrained cyclic alkenes often are less suitable substrates. An exception to this is ethylene, which reacts well. Acetylene as well as simple terminal alkynes and aryl acetylenes can be used as triple-bond component. 

Until this work, the reactions between the benzyl sulfonium ylide and ketones to give trisubstituted epoxides had not previously been used in asymmetric sulfur ylide-mediated epoxidation. It was found that good selectivities were obtained with cyclic ketones (Entry 6), but lower diastereo- and enantioselectivities resulted with acyclic ketones (Entries 7 and 8), which still remain challenging substrates for sulfur ylide-mediated epoxidation. In addition they showed that aryl-vinyl epoxides could also be synthesized with the aid of a,P-unsaturated sulfonium salts lOa-b (Scheme 1.4). 

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). 

Most of the above reactions are used for the cleavage of aryl sulphones. Recently, a note has appeared109 in which the use of potassium metal dispersed ultrasonically in toluene to cleave saturated cyclic sulphones is described. Addition of iodomethane permits the isolation of acyclic alkyl methyl sulphones (as outlined in equation (44)). 

Table 1 Reaction of chromium alkoxycarbenes with acyclic aryl aldimines...

The optimal reaction conditions were applied with 59d in the addition of various aryl boronic acids and potassium trifluoroborates to several cyclic and acyclic enones (Fig. 8). Arylboronic acids added to cyclic enones in high yields (89-97%) and with good to excellent selectivities (85-98% ee). Under these conditions, the potassium trifluoroborate reagents reacted at faster rates, but with slightly lower selectivities (83-96% ee). The reactions of acyclic enones with aryl boron reagents gave also excellent yields (83-96%). 

Hydroboration of acyclic and cyclic aryl alkenes with (Bpin) (1.1 equiv.) in the presence of NaO Bn (1-100 mol%) and MeOH (2 equiv.) is catalysed by [CuCl(NHC)], (0.5-5 mol%) NHC = Dries, SDries and ICy, and proceeds with very good conversions and regioselectivity (Scheme 2.11). 

Another approach in the use of chiral S/P ligands for the hydrosilylation reaction of ketones was proposed more recently by Evans et Thus, in 2003, these workers studied the application of new chiral thioether-phosphinite ligands to enantioselective rhodium-catalysed ketone hydrosilylation processes. For a wide variety of ketones, such as acyclic aryl alkyl and dialkyl ketones as well as cyclic aryl alkyl ketones and also cyclic keto esters, the reaction gave high levels of enantioselectivity of up to 99% ee (Scheme 10.44). 

These catalysts are believed to function through an acyclic TS. In addition to the normal steric effects of the open TS, the facial selectivity is probably influenced by tt stacking with the aryl ring and possibly hydrogen bonding by the formyl hydrogen.152... 

It has been found that a number of bidentate ligands greatly expand the scope of copper catalysis. Copper(I) iodide used in conjunction with a chelating diamine is a good catalyst for amidation of aryl bromides. Of several diamines that were examined, rra s-yV,yV -dimethylcyclohexane-l,2-diamine was among the best. These conditions are applicable to aryl bromides and iodides with either ERG or EWG substituents, as well as to relatively hindered halides. The nucleophiles that are reactive under these conditions include acyclic and cyclic amides.149... 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

Amides of phosphorous acid (e.g., P(NMe2)3 and the bicyclic compound (L16)) are useful ligands for cross-coupling of arylboronic acids with aryl bromides and chlorides (system Pd(OAc)2/2L, Cs2C03, toluene, 80 °C), the bicyclic amide being markedly more effective than simple acyclic ones.421 Amides of phosphinous acids are also excellent bidentate ligands with PN coordination mode ((L6), Section 9.6.3.4.2). 

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