Fluoro-aldehydes and ketones

Halo carbonyl compounds, a-Halo aldehydes and ketones (Continued) a-Fluoro aldehydes and ketones Fluorine, 135... 

Hai.o CAnaoNYi. toMKiUNOS. tt-Halo aWc-h)xfc and ketones a>Fluoro aldehydes and ketones Fluonnc, 135... 

Vinylalumination of Fluoro-aldehydes and Ketones. Okie of the problems of MBH reaction is the lack of reativity of p-substituted activated olefins. We applied the vinylalumination reaction reported by Tsuda and co-workers (13) for the synthesis of fluorinated MBH products (Scheme 14) (77). Due to the high reactivity of fluorinated... 

Vinylcupration of Fluoro-aldehydes and Ketones. Marino and Lindermann (20) have reported the addition of Corey s vinylcopper reagents (21) to aldehydes and ketones. We carried out vinylcupration of fluorinat aldehydes and ketones to prepare functionalized fluorinated p-substituted allyl alcohols (Scheme IS). Unlike vinylalumination, vinylcupration of fluoro-carbonyls is not stereoselective (Ktre, S. V., unpublished results). 

Alkyl- and aryl-hydrazones of aldehydes and ketones readily peroxidise in solution and rearrange to azo hydroperoxides [1], some of which are explosively unstable [2], Dry samples of the p-bromo- and p-fluoro-hydroperoxybenzylazobenzenes, prepared by oxygenation of benzene solutions of the phenylhydrazones, exploded while on filter paper in the dark, initiated by vibration of the table or tapping the paper. Samples were later stored moist with benzene at —60°C to prevent explosion [3], A series of a-phenylazo hydroperoxides derived from the phenyl-or p-bromophcnyl-hydrazones of acetone, acetophenone or cyclohexanone, and useful for epoxidation of alkenes, are all explosive [4], The stability of several substituted phenylazo hydroperoxides was found to be strongly controlled by novel substituent effects [5],... 

Huang, X.-T. Chen, Q.-Y. Ethyl a-Fluoro Silyl Enol Ether Stereoselective Synthesis and Its Aldol Reaction with Aldehydes and Ketones. J. Org. Chem. 2002, 67, 3231-3234. 

In related studies, it has been shown that a-fluorobenzylphosphonates ArCHFPO(OEt)2 (38) will undergo Wadsworth-Emmons-type olefination reactions with aldehydes and ketones [57]. 39 was prepared from benzaldehydes and HP(0) (OEt)2, which was fluorinated using diethylaminosulfur tiifluoride for example, diethyl [(3,5-dimethylphenyl)(fluoro)methyl]phosphonate (38) was formed in 91%. An 82% yield of Me 2-[(fluoro)(4-fluorophenyl)methylene]butanoate (1 1 E Z) (40) was obtained from 38 and methyl 2-oxobutanoate (Scheme 13). 

Instead to acid fluorides the reaction between trifluorovinyllithium and carbonyl compounds can lead to oc-fluoro-oc,0-unsaturated aldehydes and ketones by treating the intermediate lithium alkoholates either with a lithiumalkyl or lithium aluminium hydride, as the geminal fluoro atoms on the vinylic carbon in the alcoholates are susceptable to nucleophilic replacement by these reagents (reaction sequence (51)). Finally, rearrangement yields the a-fluoro-a,(J-unsaturated aldehydes and ketones 55). 

In a continuation of an investigation of the chemistry of P-halogeno ylids, P-fluoro ylids (29) have been shown to react with aldehydes and ketones to form 2-fluoro-l,2X -oxaphosphetans (30) which rearrange to alkylphosphonates (31). The pentaco-ordinated phosphorus compounds ( 8 P= -41.6/-56.0) were also characterised by and n.m.r. 

This method has been used for the addition of chlorofluorocarbene to trimethylsilyl enol ethers or trimethylsilyl alkyl ketene acetals. The crude products 8 were rearranged (usually without isolation) to a-fluoro-a,/ -unsaturated aldehydes and ketones or esters of a-fluoro-a,/J-un-saturated acids, respectively, in high yields. ... 

Machleidt reported the Homer-Emmons reaction of triethyl-fluoro-phosphonoacetate with aldehydes and ketones to give a-fluoro-a,p-unsaturated esters (entry 2) (76). In the case of aldehydes the reaction is highly E-selective (77), a property which was used for the preparation of fluorinated pheromones (18) and 5-fluoro-arachidonic acid (79). 

The factors affecting the competition between transesterification and olefination in reactions of phosphonoalkylcarboxylates (111) with aldehydes and potassium carbonate in alcohols under heterogeneous conditions have been investigated.57 The reaction of the carbanion of I-cyano-1-fluoromethanephosphonate, prepared in situ from diethyl cyanomethane-phosphonate (112) and N-fluorobis(trifluoromethanesulphonyl)imide, with aldehydes and ketones provides a synthesis of a-fluoro-a,3-unsaturated nitriles (113) in moderate yield (Scheme 8).5 Wadsworth-Emmons... 

Ylide and Related Reactions. AUyloxymethylenetriphenyl-phosphonium chlorides yield aUyl vinyl ethers by conversion into ylides with r-BuOK and treatment with aryl and eno-lizable acyclic aldehydes and ketones. Q , Unsaturated nitriles are obtained with high Z-stereoselectivity when diphenyl-cyanomethylenephosphonate is converted into its potassium salt by treatment with r-BuOK in THF, followed by addition of aldehydes with bulky substituents. o -Fluoro-Q, -unsaturated thia-zolines are obtained with slight l -stereoselectivity when mixtures of fluorophosphonomethylthioamides, or the corresponding thia-zolines (eq 94), and aldehydes are treated with t-BuOK in THF at 0 °C higher E-selectivity is usually observed when BuLi in THF is used as the base at —78 °C. ... 

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