Carbonyl compounds metathesis

Allylboronates are attractive reagents for the highly diastereoselective ally-lation of carbonyl compounds. A sequential cross-metathesis-allylation reaction has recently been developed by Grubbs et al. [88c] and by Miyaura et al. [103]. The sequence is illustrated in Scheme 23 for the formation of homoallylic alcohol 114 from allylboronate 112, acetal 113, and benzaldehyde [88c]. 

Oxetanes are the cycloadducts from a carbonyl compound and an olefin. This one step photochemical formation of a four membered ring heterocycle has been named the Paterno-Buchi reaction 489a> b). Oxetanes are important synthetic intermediates as they can fragment into the carbonyl-olefin pair by which they were not formed (a so termed carbonyl-olefin metathesis). Two examples of such oxetan cracking reactions are shown below in (4.76)490) and in (4.77)491) in this last example the oxetane was used as a precursor for the pheromone E-6-nonenol,... 

As noted above, titanocene-alkylidenes can be prepared using various methods and starting materials. Like the methylidene complex, higher alkylidene complexes are useful for the transformation of carbonyl compounds to highly substituted olefins. Ketones and aldehydes are converted into substituted allenes by treatment with titanocene-alkenylidenes prepared by olefin metathesis between titanocene-methylidene and substituted allenes (see Scheme 14.7) [17]. Titanocene-alkenylidene complexes can also be prepared from... 

In addition to reactions characteristic of carbonyl compounds, Fischer-type carbene complexes undergo a series of transformations which are unique to this class of compounds. These include olefin metathesis [206,265-267] (for the use as metathesis catalysts, see Section 3.2.5.3), alkyne insertion, benzannulation and other types of cyclization reaction. Generally, in most of these reactions electron-rich substrates (e.g. ynamines, enol ethers) react more readily than electron-poor compounds. Because many preparations with this type of complex take place under mild conditions, Fischer-type carbene complexes are being increasingly used for the synthesis [268-272] and modification [103,140,148,273] of sensitive natural products. 

Chromium-based reagent systems, for pinacol coupling, 11, 63 Chromium carbenes, in ene-yne metathesis, 11, 272 Chromium carbonyl compounds with bridging hydrides, 5, 206 computational studies and spectroscopy, 5, 203 experimentally determined structures, 5, 204 nitro and nitroso compounds, 5, 205 silatropic migrations, 5, 249 with very weakly bonded ligands, 5, 205 Chromium carbonyl hydrides, preparation and characteristics,... 

Metal aUcylidene complexes (see Schrock-type Carbene Complexes) have been proposed as intermediates in many catalytic reactions, including alkene metathesis (see Organic Synthesis Using Metal-mediated Metathesis Reactions), alkene and aUcyne polymerization, methylenation of carbonyl compounds, and cyclopropanation of alkenes. ... 

Over the last 50 years numerous reactions of organic compounds catalyzed by transition metal complexes have been developed (e. g., olefin oxidation -Wacker Process, hydroformylation, carbonylation, hydrogenation, metathesis, Ziegler-Natta polymerization and oligomerization of olefins) in which the reactivity of metal-carbon bonds in the active intermediate (organometallics) is crucial. 

Many methods are used for preparation of fluoroolefm precursors [11]. One of these strategies is based on Wittig-like metathesis reactions between carbonyl compounds and a-fluoroalkyl phosphoranes [12] (Scheme 2.191). 

Scheme 2.191 Synthesis of fluoro and difluoro olefins by metathesis of carbonyl compounds with fluoroalkyl phosphoranes (SBAH = sodium bis(methoxyethoxy)aluminum hydride) [12d].

Triorganylbismuthines can mediate such C-C bond forming reactions as shown in Scheme 5.38 in the presence or absence of a transition metal salt. Tributylbismuthine promotes the allylation of carbonyl compounds with allylic bromide [91HAC297] and the olefination of diazo compounds with carbonyl compounds in the presence of catalytic amounts of a copper(I) halide [90TL5897]. A combination of triphenylbismuthine and WCle promotes the metathesis of olefins, while a similar combination with TiC facilitates the stereoselective Diels-Alder reaction of unsaturated esters [76TMC183, 93JOC4783]. 

Carbonyl compounds the McMurry reaction Alkenes olefin metathesis Stereoselective Methods for E-Alkenes... 

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