Aldehydes, alkylation phenylation

Reactions of unsymmetrical methylene 1,3-dicarbonyl compounds with enol ethers have been investigated by Yamauchi et al. [137]. As we have mentioned earlier, the a,/ -unsaturated ketone moiety in alkylidene-/ -ketoesters reacts exclusively as the oxabutadiene. However, high regioselectivity is also observed with mixed alkyl-phenyl-1,3-diketones with exclusive reaction of the aliphatic carbonyl group, whereas in alkylidene-1,3-dicarbonyl compounds bearing an aldehyde and a keto-moiety, the a,/J-unsaturated aldehyde reacts preferentially as oxabutadiene, but not exclusively [130a]. 

Oxidative desulfonylation. The a-anion of alkyl phenyl sulfones on reaction with 1 is converted into aldehydes or ketones in good to high yield (equation I). 

RSeCJIi — ROCHi. Oxidation of an alkyl phenyl selenide with m-chloroperben-zoic acid (2-5 equiv.) in methanol affords the corresponding alkyl methyl ethers in high yield. Oxidation of selenides with a vicinal phenyl group is accompanied by rearrangement of the phenyl group. vtc-Methoxy selenides derived from cycloalkenes are oxidized under these conditions to dimethyl acetals of ring-contracted aldehydes. 

In 1973 Marc Juba and J.M. Paris [86] developed an olefination protocol involving three distinctive steps (Scheme 63) (1) reaction of an anion generated from alkyl phenyl sulfone 215 and n-butyllithium with an aldehyde to provide the adduct 216 (2) acetylation (or benzoylation) of 216 and (3) sodium amalgam reductive elimination of suhbnyl-ester 217. 

Chiral Ligand of L1A1H4 for the Enantioselective Reduction of Alkyl Phenyl Ketones. Optically active alcohols are important synthetic intermediates. There are two major chemical methods for synthesizing optically active alcohols from carbonyl compounds. One is asymmetric (enantioselective) reduction of ketones. The other is asymmetric (enantioselective) alkylation of aldehydes. Extensive attempts have been reported to modify Lithium Aluminum Hydride with chiral ligands in order to achieve enantioselective reduction of ketones. However, most of the chiral ligands used for the modification of LiAlHq are unidentate or bidentate, such as alcohol, phenol, amino alcohol, or amine derivatives. 

Additions to Aldehydes. Alkylation of aromatic and aliphatic aldehydes with a combination of titanium tetraisopropoxide, Ti(0-/-Pr)4, and diethy Izinc, ZnEt2, in the presence of a catalytic amount of the bis-sulfonamide la leads to formation of (S)-l-phenyl-1-propanol 4 with high enantioselectivity (eq 2, Table 1). Use of the (R,7 )-l,2-(trifluoromethanesulfonamido)-cyclohexane lb [CAS 122833-60-7] allows for an equally selective reaction, but at exceptionally low catalyst loadings. In the case of aromatic aldehydes, these reactions are fairly rapid, requiring at most 2 hours to reach full conversion. 

Phenylselenyl chloride, C HjSeCI, and phenylselenyl bromide, C Hs eBr, in connection with oxidizing agents such as hydrogen peroxide or sodium periodate, are used for the conversion of aldehydes, ketones, and esters into their a,p-unsaturated analogues. The key intermediate is alkyl phenyl selenoxide, which decomposes via a five-membered transition state [167] (equation 27). 

Cyanoselenation of aldehydes with phenyl selenocyanate in the presence of BusP gave a-(arylsele-no)nitriles. Selenylation of nitriles aSiST treatment with 2 equiv. of base also led to the formation of a-selenonitriles. Their lithiated derivatives undergo smooth alkylation with methyl iodide (80%) and Michael addition to cyclohexenone in 90% yield (Scheme 30). ... 

Lithio-2-(l-methyl-2-alkenyl)-l,3-bulky substituent on the aldehyde gave increased syn selectivity in Ae following order alkyl > phenyl > 1-silylalkenyl > alkenyl > alkynyl. Activation of an aldehyde by BP3-Et20 reduced the ratio. o ... 

The Julia olefination reaction is highly regioselective and ( )-stereoselective, providing a valuable alternative to the Schlosser reaction for making rrans -disubstituted olefins. The reaction involves condensation of a metalated alkyl phenyl sulfone with an aldehyde to yield a P-hydroxysulfone, which is then subjected to a reductive elimination to produce the alkene. There are limitations to the preparation of tri- and tetra-substituted alkenes via the sulfone route because the P-alkoxy sulfones derived from addition of the sulfone anion to ketones may be difficult to trap and isolate or they may revert back to their ketone and sulfone precursors. 

Alkyl phenyl sulfones (piCj,27) are nearly as acidic as esters hence they are readily deprotonated by n-BuLi, LDA in THF, or EtMgBr in THF to give a-metalated sulfones. Their reaction with aldehydes gives a mixture of diastereomeric P-phenylsul-fone alkoxide adducts. Reductive elimination of the benzenesulfinate moiety from the adduct to produce the alkene is usually slow. To minimize side reactions, the hydroxyl group is first converted to an acetate, benzoate, mesylate, or /7-toluenesul-fonate and then treated with an excess of sodium amalgam [Na(Hg), prepared by adding small pieces of sodium to mercury] in methanol to furnish the trans-dlk n P... 

Tab. 67 Aldehyde aus 1-Alkenen iiber Alkyl-phenyl-sulfan mit N-Chlor-succinimid...

Alkyl-phenyl-sulfane lassen sich mit N-Chlor-succinimid oxidieren, nachfolgende Hydrolyse der rohen -Chlor-phenylsulfane liefert Aldehyde. Verwendet werden zur hydrolyti-schen Spaltung ... 

The rearrangement reaction of a variety of alkyl phenyl ethers over a dealumi-nated HY zeolite has been shown to involve both intramolecular and intermolecular processes to afford phenol, (alkoxyalkyl)benzenes and alkylphenols as the main products. o-Benzylphenol has been obtained as the exclusive product in the rearrangement of benzyl phenyl ether in the presence of montmorillonite. The mechanism for a novel zeolite /3-catalysed rearrangement of alkoxybenzyl allyl ethers to aldehydes and ketones has been investigated by the use of cross-over reactions and deuterium labelling. The reaction was found to be mainly intramolecular and has been described as a nucleophilic attack of the double bond on the electrophilic benzylic carbon of the ether-Lewis acid complex, followed by a... 

Organolithiums. Allylic and benzylic alcohols undergo deoxygenative lithiation by treatment of their lithium alkoxides or phenyldimethylsilyl ethers with LDTBB. Alkyl phenyl selenides are also cleaved to give organolithium species that can react with aldehydes and allyl bromide. Some special alkyllithiums have been prepared from (2-pyridylthio)alkanes, which are available from carboxylic acids. ... 

Alkyl phenyl thioethers RCH2SPh are available by radical-initiated addition of benzenethiol to a terminal olefin or by reaction of an alkyl bromide with thio-phenoxide ion. N -Chlorosuccinimide effects halogenation at the a-site, and the a-chloroalkyl thioether gives the corresponding aldehyde RCHO on treatment with mercury(ll) chloride and cadmium(ll) carbonate in aqueous carbon tetra-... 

Reduction of a-silyl sulfides with tributylstannyllithium is also useful for the generation of a-silyl carbanions [251]. When a,a-bis(trimethylsilyl)alkyl phenyl sulfides 137 are treated sequentially with tributylstannyllithium and aldehydes, they give the corresponding alkenylsilanes (Scheme 2.87). This method has an advantage in that tributylstannyllithium is thermally stable and can be stored for several months. 

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