Aldehydes with metal alkyls

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

C-C bonds can be formed by reaction with alkyl iodides or more usefully by reaction with metal carbonyls to give aldehydes and ketones e.g. Ni(CO)4 reacts with LiR to form an unstable acyl nickel carbonyl complex which can be attacked by electrophiles such as H+ or R Br to give aldehydes or ketones by solvent-induced reductive elimination ... 

Chiral oxazolines developed by Albert I. Meyers and coworkers have been employed as activating groups and/or chiral auxiliaries in nucleophilic addition and substitution reactions that lead to the asymmetric construction of carbon-carbon bonds. For example, metalation of chiral oxazoline 1 followed by alkylation and hydrolysis affords enantioenriched carboxylic acid 2. Enantioenriched dihydronaphthalenes are produced via addition of alkyllithium reagents to 1-naphthyloxazoline 3 followed by alkylation of the resulting anion with an alkyl halide to give 4, which is subjected to reductive cleavage of the oxazoline moiety to yield aldehyde 5. Chiral oxazolines have also found numerous applications as ligands in asymmetric catalysis these applications have been recently reviewed, and are not discussed in this chapter. ... 

Variations and Improvements on Alkylations of Chiral OxazoUnes Metalated chiral oxazolines can be trapped with a variety of different electrophiles including alkyl halides, aldehydes,and epoxides to afford useful products. For example, treatment of oxazoline 20 with -BuLi followed by addition of ethylene oxide and chlorotrimethylsilane yields silyl ether 21. A second metalation/alkylation followed by acidic hydrolysis provides chiral lactone 22 in 54% yield and 86% ee. A similar... 

The organic analogues of the reactions to be discussed here are the borane reductions of aldehydes and ketones and the addition of metal alkyls across ketonic carbonyls, equation 15. In contrast to the ease of these organic reactions, qualitative data which has accumulated in our laboratory over the last decade demonstrates that the carbonyl group in organometallies is fairly resistant to addition across CO. For example, many stable adducts of organometallie carbonyls with aluminum alkyls are known, eq. lc, but under similar conditions a ketone will quickly react by addition of the aluminum alkyl across the CO bond. A similar reactivity pattern is seen with boron halides. 

Nucleophilic addition of metal alkyls to carbonyl compounds in the presence of a chiral catalyst has been one of the most extensively explored reactions in asymmetric synthesis. Various chiral amino alcohols as well as diamines with C2 symmetry have been developed as excellent chiral ligands in the enantiose-lective catalytic alkylation of aldehydes with organozincs. Although dialkylzinc compounds are inert to ordinary carbonyl substrates, certain additives can be used to enhance their reactivity. Particularly noteworthy is the finding by Oguni and Omi103 that a small amount of (S)-leucinol catalyzes the reaction of diethylzinc to form (R)-l-phenyl-1 -propanol in 49% ee. This is a case where the... 

The metalation of vinyl ethers, the reaction of a-lithiated vinyl ethers obtained thereby with electrophiles and the subsequent hydrolysis represent a simple and efficient method for carbonyl umpolung. Thus, lithiated methyl vinyl ether 56 and ethyl vinyl ether 54, available by deprotonation with t- or n-butyllithium, readily react with aldehydes, ketones and alkyl halides. When the enol ether moiety of the adducts formed in this way is submitted to an acid hydrolysis, methyl ketones are obtained as shown in equations 72 and 73 . Thus, the lithiated ethers 56 and 54 function as an acetaldehyde d synthon 177. The reactivity of a-metalated vinyl ethers has been reviewed recently . 

The procedure described here provides a convenient route to aldehydes with trithiane serving as an inexpensive, masked carbonyl group.2-4 The reaction is limited, however, to the use of primary alkyl halides, aldehydes, and ketones for elaboration of the carbon chain through attack on the metallated trithiane. Examples of aldehydes synthesized by this method are given in Table I. 

Concurrent with acetic anhydride formation is the reduction of the metal-acyl species selectively to acetaldehyde. Unlike many other soluble metal catalysts (e.g. Co, Ru), no further reduction of the aldehyde to ethanol occurs. The mechanism of acetaldehyde formation in this process is likely identical to the conversion of alkyl halides to aldehydes with one additional carbon catalyzed by palladium (equation 14) (18). This reaction occurs with CO/H2 utilizing Pd(PPh )2Cl2 as a catalyst precursor. The suggested catalytic species is (PPh3)2 Pd(CO) (18). This reaction is likely occurring in the reductive carbonylation of methyl acetate, with methyl iodide (i.e. RX) being continuously generated. 

Thus, the characteristic potentiometric selectivity of calix[6]arene hexaester 29 for primary amine guests can be reasonably interpreted on the basis of the structural factors relevant to the nonpolar moieties of guests. Such a mode of discrimination can also be achieved by a calix[6]arene hexaester with short alkyl chains [28 (R = H)]. In addition, the selectivity was found to be essentially the same in the presence or absence of lipophilic anionic site HFPB added in the membrane (Table 3). Potentiometric discrimination of protonated amines by host 28 (R = H, Bu ) as well as of aldehydes (as the protonated hydrazones generated in situ) by hosts 26 (R = Bu ) and 28 (R = H) was also reported. Recently, quantitative estimation of optical selectivities for alkali metal ions or protonated amines were made with liquid membranes containing chromogenic derivatives of calixarenes. ... 

Many compounds have been tested as ignition quality improvers—additives which shorten the ignition delay to a desirable duration. An extensive review in 1944 (6, 43) listed 303 references, 92 dealing with alkyl nitrates and nitrites 61 with aldehydes, ketones, esters, and ethers 49 with peroxides 42 with aromatic nitro compounds 29, with metal derivatives 28 with oxidation and oxidation products 22 with polysulfides 16 with aromatic hydrocarbons nine with nitration and four with oximes and nitroso compounds. In 1950, tests at the U. S. Naval Engineering Experiment Station (48) showed that a concentration of 1.5% of certain peroxides, alkyl nitrates, nitroaikanes, and nitrocarbamates increased cetane number 20 or more units. 

The great synthetic utility of the reaction of alkyllithium and Grignard reagents with ketonic functions has been well documented.105 These reactions take place via the intermediacy of alkoxy derivatives formed by addition of the M—C bond across the C=0 function. Hence ketones, aldehydes and formaldehyde will lead to tertiary, secondary and primary alkoxides, respectively. This type of reactivity is known for a number of other carbanionic metal alkyl derivatives, both main group and transition metals, although the synthetic utility of the reactivity has in most cases not been well documented. 

Furukawa et al. [274] and Natta cl al. [275,276] succeeded independently in the preparation of crystalline polyacetaldehyde by using some organometallic compounds, such as diethylzinc or triethylaluminium, for the low-temperature polymerisation of acetaldehyde. Metal alkyls and metal alkoxides, e.g. aluminium isopropoxide, zinc ethoxide or ethyl orthotitanate, have also polymerised other aldehydes such as propionaldehyde and trichloroacetaldehyde to give crystalline polymers (Table 9.3) [270,275,277], A highly crystalline isotactic polymer has been obtained from the polymerisation of w-butyraldehyde with triethylaluminium or titanium tetrachloride-triethylaluminium (1 3) catalysts. Combinations of metal alkyl, e.g. diethylzinc, with water [278] or amine [279] appeared to give very efficient catalysts for aldehyde polymerisations. 

Zinc and cadmium alkyls have not been successful as stereospecific catalysts in the absence of co-catalysts, presumably because they do not complex strongly enough with the monomer and the metal-carbon bonds are too covalent. Cadmium alkyls were first reported by Furukawa and coworkers (260) to induce vinyl polymerization, but it was shown later (267, 262) that oxygen was a co-catalyst and the reactions were free radical in nature. Similar free radical results were obtained with zinc alkyls (261—263) and vinyl monomers. However, with more basic and more easily polarized monomers, such as olefin oxides and aldehydes, the zinc catalysts operate by a coordinated anionic mechanism (250). 

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