Aldehydes methylenation

FRIEOLANOER Quinoline Synthesis Quinoline synthesis from condensation of o aminoaryl aldehydes (ketones) with a methylene aldehydes (ketones)... 

The aldehyde group of laevulinic aldehyde reacted preferentially with the ester phosphorane (38), while the 2-acetyl groups of the benzofurans (39) were selectively methylenated with methylenetriphenylphosphorane. The aldehyde group was protected as the dimethylacetal in the synthesis of the steroidal a-methylene-aldehyde (40). 

Iodine-Mercury(II) oxide, 149 a-METHYLENE ALDEHYDES AND KETONES 1,4-Diazabicyclo[2.2.2]octane, 92 Dimethyl sulfoxide, 124 Formaldehyde, 136 Methoxyallene, 177 Methylene cycloalkanes By cyclization reactions Diacetatobis(triphenylphos-phine)palladium(II), 91 l-Hydroxy-3-trimethylsilylmethyl-3-butene, 147... 

Fig. 12.14. Aminomethyla-tion of an aldehyde via its enol (C) ("Mannich reaction"). This transformation can then be employed (as shown) to obtain an a-methylenated aldehyde...

Methylene aldehydes are also readily accessible by way of the Mannich bases thus... 

NMR absorption spectra are characterized by the chemical shift of peaks and spin-spin splitting of peaks. Recall that the chemical shift is caused by the drifting, not orbiting or spinning, of nearby electrons under the influence of the applied magnetic field. It is therefore a constant depending on the applied field (i.e., if the field is constant, the chemical shift is constant). The chemical shift therefore identifies the functional group, such as methyl, methylene, aldehydic H, aromatics, and so on (see Table 3.3). All proton spectra shown have TMS as the reference, with the TMS absorbance set at 0.0 ppm. The smdent should note that all of the 300 MHz proton NMR spectra provided by Aldrich Chemical Company, Inc. also include the 75 MHz C spectmm at the top. C NMR spectra are discussed in Section 3.6.4. 

Formylamines s. Formamides C-Formyiation (s. a. C-Hydroxy-methylenation, Aldehyde groups, introduction) 20, 600 —, o-formylation, preferential, of phenols 20, 558 N-Foriiiylation... 

Methylenation with 56a is typically performed by adding the carbonyl compounds to a solution of the reagent prepared in situ (Table 4.17). This methylenation is of interest in that the reaction is extremely sensitive to steric hindrance. The molybdenum compound 56a methylenates aldehydes such as heptanal and ben-zaldehyde. Although 56a methylenates acetophenone, diethyl ketone and henzo-phenone are not transformed to the corresponding terminal olefins. Thus, a molecule containing both ketone and aldehyde fimctions is selectively methylenated only at the aldehyde carbonyl (entry 3). 

Similar treatments of Cl3(0)Mo, (EtO)3MoCl2, and (EtO)2MoCl3 with methyl-lithium afford the corresponding molybdenum-methylidenes 56b, 56c, and S6d, which also methylenate aldehydes [122]. As regards the structure of 56b, later investigations indicated it to be the dimeric l,3-dioxo-l,3-dimolybdenum(V) cydo-butane complex, similar to S6a [124]. The reactivity order of these reagents for... 

It is noteworthy that aldehydes and ketones can be methylenated in aqueous or ethanohc media with the molybdenum compounds S6a and S6b [125]. The yields of the olefins obtained by the reactions with 56b carried out in EtOH are virtually the same as those obtained using anhydrous and alcohol-free THE as the solvent. The reagent 56a also methylenates aldehydes in aqueous or ethanohc solvents, but the yields of the olefins are lower. These methods seem to be advantageous for the olefination of hydrophilic substrates. 

The complex 56b exhibits high selectivity in that it methylenates aldehydes in preference to ketones. Hydroxyl and amino groups in the substrates are tolerated in the methylenation using 56b, whereby a unique chemoselectivity is observed the carbonyl group in a /1-hydroxy ketone is preferentially methylenated in competition reactions with simple ketones or y8-methoxy or dimethylamino ketones (Scheme 4.55) [126],... 

Formylamines s. Formamides C-Formylation (s. a. Hydroxy-methylene. . ., Aldehyde group, introduction) 16, 797 N-Formylation, preferential 16, 421... 

---