Olefins disubstituted functionalized

The complex [Ir(cod)(L)]BarF, (cod= 1,5-cyclooctadiene BArp = tetrakis[bis-3,5-(trifluorome thyl)phenyl]borate and L = (250) or (251)), has been used in asymmetric hydrogenation of several E- and Z-trisubstituted and disubstituted functionalized olefins. The proper choice of ligand components gave up to 99% ee under unoptimized reaction conditions. ... 

The utility of Ru-catalyzed cross-metathesis in multicomponent coupling strategies has also been demonstrated. For instance, one-pot cross-metathesis/allylboration sequences have been reported by Miyaura [170] and by Goldberg and Grubbs [171]. Pinacol allyl boronate 174 was reacted with a series of functionalized olefins, which include symmetrically 1,2-disubstituted olefins as well as hindered olefins and styrenes, in the presence of catalyst 175 to produce intermediate allyl boro-nates (e.g. 176). The latter may then be reacted in situ with aldehydes to produce functionalized homoallylic alcohols with high levels of anti-selectivity (Scheme 8.80). 

This synthetic sequence for an olefin synthesis has been further developed by Kocienski who has shown that eliminative desulphonylations carried out on / -acyloxysulphones are remarkably stereoselective for the synthesis of trans-disubstituted-olefins. The method has wide applicability in that a-lithio phenyl sulphones are readily generated, and are readily coupled to aldehydes or ketones, to give j8-hydroxysulphones. The hydroxyl function of these is then esterified and the synthesis is completed by the reductive elimination with sodium amalgam. Kocienski has prepared two reviews that summarize his syntheses of a range of natural products - one of which is diumycinoP obtained... 

Katritzky offers a general one-pot alternative approach to polysubstituted pyrroles utilizing disubstituted olefins of which a wider variety is commercially available compared to acetylenes . Thus, thioamides 32 were subjected to Mannich condensation with aldehydes and BtH to yield functionalized thioamides 33 which were then treated with base... 

In contrast with olefins, alkoxy-alkoxycarbonylation of alkynes to give /J-alkoxyacrylic esters is not a common reaction, and has occasionally been observed as a side reaction of the main reaction pathway leading to maleates and fumarates [77,80]. However, with suitably functionalized alkynes bearing a coordinating group (such as o ,a -disubstituted propargylic acetates) it may become the major reaction course (Scheme 15) [88]. 

The triethylsilyl trioxide reacts smoothly with internal disubstituted olefins to give potent antimalarial 1,2,4-trioxanes, especially when there is oxygen functionality in the molecule (equation 84). 

Ab initio calculations also confirm that the use of an allyl magnesium alkoxide in place of the alcohol functionality will lead to high or complete stereoselectivity (138). When homoallylic alcohols are used, the Kanemasa protocol afforded the respective isoxazolines with poor stereoselectivity ( 55 45) in the case of terminal aUcenes, but with very high diastereoselectivity (up to 96 4) in the reaction of cis-1,2-disubstituted olefins (136). Extension of this concept to the reaction of a-silyl allyl alcohols also proved feasible and produced the syn (threo) adducts as nearly pure diastereomers (>94 6) (137). Thus, the normal stereoselectivity of the cycloaddition to the Morita-Baylis-Hillman adducts (anti > syn, see above) can be reversed by prior addition of a Grignard reagent (176,177). Both this reversal... 

Additions to functionalized three-carbon olefins have been studied extensively. We have used methyl acrylate as a standard olefin since it always reacts only at the terminal carbon and the a,/3-double bond in the product is always trans. The stereospecificity of its reactions with vinylic halides varies with structure. The simple 1-halo-l-alkenes with methyl acrylate under normal conditions give mixtures of E,Z- and E,E-dienoates. The reaction is more selective with the bromides than with the iodides and the stereoselectivity increases with increasing triphenylphosphine concentration. This occurs because the excess phosphine displaces the hydridopalladium halide group from the diene 7r-complex before readdition to form the ir-allylic species occurs (see Equation 6). The disubstituted vinylic bromides react stereospecifically with methyl acrylate (4). 

The substrate scope of this epoxidation was subsequently investigated using a variety of olefins with a catalytic amount of ketone 1 (usually 20-30 mol%). A variety of hms-substituted and trisubstituted olefins have been shown to be effective substrates (Table 10.1),39 and the high ee obtained with hms-7-tetradecene suggests that this epoxidation is quite general for simple trans-olefins (Table 10.1, Entry 5). Various functional groups such as ethers, ketals, esters, and so on are compatible with the epoxidation conditions (Table 10.1). A variety of 2,2-disubstituted vinylsilanes... 

The relative rates of the cobalt-catalyzed silyl peroxidation reactions were determined for different substitution patterns of 337. Terminal alkenes are the least reactive substrates. The reaction is sensitive to steric factors. 1,1-Disubstituted olefins convert most easily, while tri- and tetrasubstituted alkenes transform more slowly. Both electron-rich and electron-poor alkenes are substrates in the silyl peroxidation however, both types react more slowly than styrenes [379]. These reaction conditions were also applied to the silyl peroxidation of several 1,1-disub-stituted alkenes bearing alcohol or peroxy functionalities in the molecule [380]. 

Very recently it was shown that sulfonyl oximes 359 are suitable reagents for the addition of oxime functions to olefins 355 (entry 22) [403]. This C-C bond-forming reaction proceeded for a wide range of terminal and 1,1-disubstituted substrates with formal Markovnikov selectivity using catalytic amounts of 357a. Branched oximes 360 were isolated in 33-95% yield. 

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