Ketones continued synthesis

Synthesis.— Type A S—C—N + C—C). The formation of thiazoles by the reaction of thiourea and its derivatives with a-halogenated ketones continues to be a popular synthetic method, whilst aryl(dichloromethyl)carbinols, bis(chloronitroso)-compounds, and a-chloro-epoxides have also been utilized. 

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Cyclization—Continued a-diketone and ketone to a cyclo-pentadienone, 23, 92 indole synthesis, 23, 42 ketone phenylhydrazone to indole, 22, 98... 

In recent years, dioxiranes have become workhorses for a variety of selective transformations in organic synthesis, from epoxidation of alkenes to the conversion of alcohols into fee corresponding ketones <99CJC308>. Dioxirane-mediated epoxidation continues to be the method of choice for complex substrates wife acid-sensitive functionality. Thus, fee dimethyl-dioxirane (DMD)-mediated epoxidation of the silylated stilbene lactam 159 has been reported as a key step in fee synthesis of protoberberines <99JOC877>. 

In continuation of our investigations on asymmetric nucleophilic acylations with lithiated a-aminonitriles [40], we envisaged the asymmetric synthesis of 3-substituted 5-amino-4-oxo esters A, bearing both a-amino ketone and 5-amino ester functionalities (Scheme 1.1.14) [41]. Since a-amino ketones are precursors of chiral p-amino alcohols [42, 43] and chiral amines [43], their asymmetric synthesis has the potential to provide valuable intermediates for the synthesis of biologically active compounds, including peptidomimetics [44]. The retrosynthetic analysis of A leads to the a-aminoacyl carbanion B and p-ester carbocation... 

In continuation of our efforts to explore the utility of the SAMP/RAMP hydra-zone methodology, we developed the first asymmetric synthesis of a-phosphino ketones via formation of a carbon-phosphorus bond in the a-position to the carbonyl group [70]. The key step of this asymmetric C—P bond formation is the electrophilic phosphinylation of the ketone SAMP hydrazone 87, giving rise to the borane-adduct of the phosphino hydrazone 88 with excellent diastereoselectiv-ity (de = 95-98%). Since these phosphane-borane adducts are stable with respect to oxidation, the chemoselective cleavage of the chiral auxiliary by ozonolysis leading to the a-phosphino ketones (R)-89 could be accomplished with virtually no racemization. Using RAMP as a chiral auxiliary, the synthesis of the enantiomer (S)-89 was possible (Scheme 1.1.25). 

Improvements in the double Skraup synthesis of 1,7-phenanthroline from m-phenylenediamine now enable a yield of 70% to be achieved.163 The Skraup reaction continues to be used for the synthesis of 1,7-phen-anthrolines starting from the substituted 5-aminoquinolines. S-Chloro-6-hydroxy-1,7-phenanthroline (18) has been prepared in this way,164 and an improved synthesis of 6-hydroxy-1,7-phenanthroline was reported.165 As expected, the Skraup reaction on 5-aminoquinaldine affords 8-methyl-1,7-phenanthroline,166 not 2-methyl-1,7-phenanthroline as it was previously named.8 The extension of the Skraup reaction using methyl vinyl ketone instead of glycerol has been applied to 5-aminoquinoline to afford 4-methyl-1,7-phenanthroline.166 A related condensation using 2-hydroxymethylenecyclohexanone provides a route to benzo-substituted 1,7-phenanthrolines.167 7-Aminoquinoline with mesityl oxide in the presence of iodine gives 8,8,10-trimethyl-7,8-dihydro-l,7-phenanthroline (19).168... 

---