Aldehydes diimide

An alternative approach was also briefly investigated Scheme 3.29). Condensation of the aldehyde (151), readily available from (150) [104], with l-chloro-3-(triphenylphosphoranylidene)-2-propanone afforded (152), which was reduced to (153) with diimide. This approach was abandoned in light of the poor yields obtained for both (152) and (153). 

Mono-benzoyldiimides such as 177 behave in a relatively normal manner, reaction with the pyrrolidine enamine of cyclohexanone (or cyclopentanone) giving the oxadiazine 178355 (Scheme 181). Reaction of dimethyl azodicarboxylate with / -disubstituted aldehyde enamines is reported to give the 1,2-diazetidine 179 and hence the aldehyde 180 on hydrolysis356", dibenzoyldiimide gives the oxadiazine 1813566 (Scheme 181). The ethoxycarbonyl aroyl diimide 182 reacts to give oxadiazine 183 exclusively357 (Scheme 182). 

Dimethyl sulfoxide (DMSO), which is successfully used to dehydrogenate primary alcohols to aldehydes, converts secondary alcohols into ketones in very high yields and under very gentle conditions. The mechanism is discussed in a previous section. Dehydrogenation and Oxidation of Primary Alcohols to Aldehydes (equation 217). The first oxidations were carried out in the presence of dicyclohexylcarbodiimide and an acid catalyst such as pyridinium trifluoroacetate [1016], which protonates the diimide and facilitates the attack by dimethyl sulfoxide (equation 259). 

The nitronate anion derived from nitro sugar 82, available from glucopyranoside 1 using standard methods, condenses with aldehyde 33 to afford adduct 83. Reduction with diimide of the ii-olefin, produced in low yield by radical elimination of the nitroaldol, and removal of the... 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Reaction of methyl j8-aminocrotonate (LXXVI) with thiophosgene under the catalysis of triethylamine led to the formation of LXXVII. A possible mechanism is shown above. Deuteration studies showed that C-5 has a considerable amount of anionic character, a property utilized later in the synthesis. Treatment of LXXVII with A-bromosuccinimide provided LXXVIII. Subsequent formation of the Wittig reagent with triphenylphosphine and reaction with 3,4,5-trimethoxybenzaldehyde gave LXXIX. The styrene double bond was selectively reduced with diimide and the carbomethoxy group transformed into an aldehyde... 

An N-protected amino aldehyde can be prepared by Swem oxidation of an N-pro-tected amino alcohol in the presence of an oxidizing agent comprising DMSO and a water-soluble carbodiimide derivative as l-ethyl-3-(3-dimethylaminopropyl)carbo-diimide hydrochloride (EDC) in an organic solvent. The N-protected amino alcohol can be derived from an L-, D-, or L-/D-amino acid, but usually is the N-protected-(S)-a-amino alcohol derived from an N-protected L-amino acid. 

One of the popular and widely used methods for the synthesis of 2-trifluoromethylimidazole involves the Radziszewski reaction (Debus-Radziszewski reaction) [2a]. Following the Davidson s modifications (using ammonium acetate in acetic acid instead of ammonia in alcohol) [13a], Lombardino and Wiseman prepared a series of 2-trifluoromethylimidazoles via the condensation of a-dicarbonyl compounds and trifluoroacetaldehyde ethyl hemiacetal (Scheme 4) [13b]. The reaction presumably proceeds via the formation of a diimide intermediate that subsequently undergoes condensation with the aldehyde to afford the final product. An anhydrous condition is highly recommended for better yields of imidazoles. 

In 2009, Chen and coworkers reported a highly enantioselective organocatalytic inverse electron demand HDAR reaction of o-benzoquinone diimides and aliphatic aldehydes catalyzed by a,a-diphenylprolinol (9-TMS ether 269 as a chiral secondary amine (Scheme 2.40) (Li et al. 2009b). 

Scheme 2.41 Asymmetric inverse electron demand HDAR of o-benzoquinone diimides 268 and aldehydes 253...

The scope of this asymmetric HDAR was evaluated under the optimized reaction conditions using o-benzoquinone diimide 268. Since the hemiaminal 270 was not stable enough for further analysis, PCC (pyridinium chlorochromate) oxidation was employed to produce the more stable quinoxalinones 271. As shown in Scheme 2.41, a variety of aldehydes 253 bearing simple linear or branched a-substituted alkyl groups were well tolerated and excellent enantioselectivities were generally obtained. 

J-L, Han B, Jiang K, Du W, Chen Y-C (2009b) Organocatalytic enantioselective hetero-Diels-Alder reaction of aldehydes and o-benzoquinone diimide synthesis of optically active hydroquinoxalines. Bioorg Med Chem Lett 19(14) 3952-3954. doi 10.1016/j.bmcl. 2009.03.013... 

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