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Enones Lewis bases

Further work by the Ye group has shown that NHCs derived from pre-catalyst 215 can also promote the asymmetric dimerisation of alkylarylketenes 193 to generate alkylidene P-lactones 216 in good diastereo- and enantio-selectivity [83], The asymmetric [4+2] addition of enones and alkylarylketenes to generate 8-lactones 218 in high ee has also been accomplished [84], as has the asymmetric esterification of alkylarylketenes to give esters 217 using benzhydrol, which is assumed to proceed via a Lewis-base mediated mechanism (Scheme 12.46) [85]. [Pg.287]

Addition of azide ion to conjugated systems can be carried out by using NaN3 and acetic acid in water (Eq. 10.18).38 Some reactions were very rapid while others took 1 to 3 days to complete. Lewis base was found to catalyze such conjugate additions of azide ion to cyclic enones in water.39... [Pg.320]

Finally, it is noteworthy that Lewis base adducts of gallane (I.GalL) reduce cyclic ketones, enones and w-haloketones to the corresponding alcohols in excellent yields254. These reagents show some promise as a new extension of the boron-type reductions of carbonyl compounds. [Pg.724]

Chiral BINOL (60) is a bifunctional organocatalyst in addition to the phenolic Brpnsted acid groups, it has a Lewis base unit attached via a spacer moiety.167 This particular combination holds the groups in a conformational lock, where they can doubly activate a substrate while giving a high level of stereocontrol. For this example of an aza-Morita-Baylis-Hillman reaction of an enone and an imine, yields up to 100% and ees up to 96% have been achieved. [Pg.22]

In 2008, Ye and coworkers also developed a new type of multifunctional cinch-onidine-based catalyst, such as 119 having an additional primary amine moiety, for the Michael addition of nitroalkane to cydic enones [32], In the presence of an acid cocatalyst, the primary amine moiety of 119 can act as a Lewis base to activate the Michael acceptor via iminium formation. The catalysts 119a and 119b (5 mol%) provided quite excellent enantioselectivity (up to 98% ee) for the Michael addition of nitroalkanes to cyclohexenone (Scheme 9.40). The observed retardation of the reaction rate and the opposite sense of enantioselectivity obtained with the catalyst 119b indicated the importance of the configuration of the cydohexane... [Pg.273]

Aldol reaction. TrichlorosiloxyaUcenes are generated in a dehrominative silylation process from a-bromo ketones. Condensation with ArCHO leads to p-aryl enones. In the presence of the Lewis base Ph3PO the reaction is optimized. [Pg.247]

Reaction with Cyclic Enones. Conjugate addition of azide ion to cyclic enones in water using sodium azide in the presence of Lewis base resulted in the formation of 8-azido carbonyl compounds (eq 55). The Schmidt reaction of benzopyranones with sodium azide led to pyrano[3,2-b]azepines in reasonable yields (eq 56). [Pg.403]

Cheng et al. have developed the first example of a stoichiometric weak Lewis base, imidazole, catalyzed MBH reaction between cyclic enones and aromatic aldehydes in aqueous media. At the same time, Gatri and El Gaied" also independently reported the MBH reaction of cycloalkenones with various aldehydes, including ahphatic and aromatic aldehydes, by using catalytic quantities imidazole as catalyst in aqueous media (Scheme 2.45). [Pg.98]

When we extended the activated olefins to cyclohept-2-en-l-one and cyclooct-2-en-l-one we found that the reaction is very complicated, because the Lewis bases, solvents and the ring-size of the cyclic enone can all significantly affect the MBH reaction rate and even the reaction product. The reaction of cyclohept-2-en-l-one with A-arylidene-4-methylbenzenesulfonamides afforded the usual MBH adducts 203 along with abnormal adducts 204, whereas the corresponding reaction of cyclooct-2-en-l-one provided different aldol products (205-207) depending upon the Lewis base employed (no MBH adduct was formed in any of the cases) (Scheme 2.104). Moreover, the formation of aldol products 209 along with the usual MBH adducts 208 has been observed in the reaction between cyclopent-2-en-l-one and aromatic aldehydes in the presence of BU3P (Scheme 2.105). [Pg.127]

The Spiro-type Brpnsted acid-Lewis base (199) has been shown to catalyse the aza-MBH reactions of a-enones CH2=CHCOR and imines R CH=NTs with <98%... [Pg.416]

In a related manner, N-acylated P-amino enones experienced reductive cycliza-tion under the catalysis of a chiral Lewis base to preferentially furnish enantioen-riched 4H-l,3-oxazines, where trichlorosilane acted not only as a reductant but also as a dehydrating agent [35], The selectivity of 9 was revealed to be superior to that of SEGPHOS-derived 10 (Scheme 7.20). [Pg.170]

As an alternative, tin enolates are very useful in these additions. Usually they are prepared in situ from the amide using tin(II) trifluoromethanesulfonate and a base. They are subsequently reacted with an enone, catalyzed by a Lewis acid47-48 (see Table 3). With triinethylsilyl trifluoromethanesulfonate as a catalyst, in the presence of proline derived diamines anti-adducts are formed exclusively49 (see Section 1.5.2.4.3.1.). [Pg.959]

Ferrocen-l,l -diylbismetallacycles are conceptually attractive for the development of bimetal-catalyzed processes for one particular reason the distance between the reactive centers in a coordinated electrophile and a coordinated nucleophile is self-adjustable for specific tasks, because the activation energy for Cp ligand rotation is very low. In 2008, Peters and Jautze reported the application of the bis-palladacycle complex 56a to the enantioselective conjugate addition of a-cyanoacetates to enones (Fig. 31) [74—76] based on the idea that a soft bimetallic complex capable of simultaneously activating both Michael donor and acceptor would not only lead to superior catalytic activity, but also to an enhanced level of stereocontrol due to a highly organized transition state [77]. An a-cyanoacetate should be activated by enolization promoted by coordination of the nitrile moiety to one Pd(II)-center, while the enone should be activated as an electrophile by coordination of the olefinic double bond to the carbophilic Lewis acid [78],... [Pg.159]


See other pages where Enones Lewis bases is mentioned: [Pg.140]    [Pg.140]    [Pg.245]    [Pg.178]    [Pg.726]    [Pg.165]    [Pg.17]    [Pg.150]    [Pg.23]    [Pg.24]    [Pg.129]    [Pg.198]    [Pg.419]    [Pg.2928]    [Pg.112]    [Pg.21]    [Pg.346]    [Pg.15]    [Pg.925]    [Pg.925]    [Pg.233]    [Pg.334]    [Pg.1030]    [Pg.76]    [Pg.4]    [Pg.243]    [Pg.333]    [Pg.233]    [Pg.334]    [Pg.384]    [Pg.384]    [Pg.233]    [Pg.334]   
See also in sourсe #XX -- [ Pg.543 ]




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Bases. enones

Enones Lewis base catalysis

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