Catalytic hydrogenation conditions

It was assumed that pyridine derivative 181 yielded pyrido[l,2-c]pyrimidine betaine 182 under catalytic hydrogenation conditions over (5,S)-Et-DuPHoS-Ph catalyst (99TL1211). 6,7-Dehydro derivative 184 of trequinsin (3) was obtained from pyrimidinone 183 by heating in an 1 1 mixture of MeOH and cone. HCl under reflux (97IJC(B)349). 

If we compare these productivities with those obtained under catalytic hydrogenation conditions (Table 2, Figure 3), we can see that the trend is different Cu/MgO shows very low activity, particularly if compared with that of the catalyst supported on silica and modified silicas. 

Geraniol can be converted into citronellol and menthol over Cu/A1203 under catalytic hydrogenation conditions owing to chemoselective hydrogenation and a three-functional process taking place on the catalyst surface. 

Here we report that geraniol 1, under catalytic hydrogenation conditions in the presence of a Cu/A1203 catalyst, gives two valuable products, namely citronellol 2 and menthol 3. 

Experimental data published recently by Cudmore (10) for eight Australian bituminous coals, reproduced in Fig. 2, show a direct linear correlation between conversion (to gas + liquids), under non-catalytic hydrogenation conditions using Tetralin as... 

Studies initiated by the author in CSIRO (13) seek to throw light on the role of the various macerals by studying the conversion, under catalytic hydrogenation conditions, in Tetralin as vehicle, of maceral concentrates from a high volatile bituminous coal. Some preliminary results, given in Fig. 3, show conversions as almost complete for the hand picked vitrain (>90% vitrinite) from a high volatile bituminous coal (Liddell seam N.S.W., 83.6% carbon and 43% volatile matter both expressed on a dry ash-free basis). However, it is evident that the conversion of the whole coal increases rapidly with increase in hydrogen pressure (under otherwise similar conditions - batch autoclave, 4h. 400°C). 

Treatment of 8-azidomethylperhydropyrido[l,2-f]pyrimidin-l-one 127 with MeOTf and catalytic hydrogenation of the azide group led to the formation of the tricyclic guanidine derivative 128 (Equation 23) <2001JA8851, 2002JA3939>. A similar tricyclic compound was prepared from an 8-azidomethyl-l-methoxy-4,4a,5,6,7,8-hexahy-dro-37/-pyrido[l,2-f]pyrimidine under catalytic hydrogenation conditions over Pd/C catalyst <2002JA4950,... 

Scheme 5.4 Three processes in which nickel diphosphane complexes can be involved under catalytic hydrogenation conditions. (A) ligand exchange (B) oxidation and (C) hydrogenation of 1-octene. For simplicity, the reac-...

Epiaphylline was isolated ftomLupinus hartwegii (146-147). The mass spectrum of this alkaloid is characterized by peaks at m/z 248 (70), 247 (46), 220 (45), 137 (47), 136 (100), 97 (53), and 96 (45%) that are tyical for sparteine alkaloids. The peak at m/z 220 originates from the splitting of a carbonyl group. Epiaphylline (110), in contrast to aphylline (108), did not react under mild catalytic hydrogenation conditions, but under harsher conditions epiaphylline (110) converted to 3-isosparteine (14) (Scheme 14). This established the presence of a carbonyl group at C-10. 

A double reduction was achieved under catalytic hydrogenation conditions to open the epoxide and reduce the nitro group to an amino group in 90% yield. The aniline thus afforded was reacted with diethylethoxymethylenemalonate to give 92. 92 was next cyclized to the 1,4-benzoxazine 93 via a Mitsunobu reaction in the absence of a Lewis acid, unlike Kim s approach (Kang et al., 1996). Completion of the tricycle core was ultimately achieved in PPE at 140-145°C to furnish the LVX core in 85% yield. The core was converted to LVX (1) in two precedented steps. 

Partially reduced pyrimido[4,5-f][l,2]oxazines prove to be robust to catalytic hydrogenation conditions, in the preparation of a tritiated nucleoside analogue (Equation 130) <1997W097/28177>. 

In a related synthetic study, the alcohol 16 was hydrogenated over 5% palladium on charcoal in hexane to provide sj/ -tricyclo[4.2.1.125]dec-3-en-8-ol (17) in 98% yield.44 As can be seen in the following scheme, the common bond of the two cyclobutane rings is again the most vulnerable towards catalytic hydrogenation conditions. 

Once the porphyrin ring is open, the metal is deposited on the catalyst. Open chain tetrapyrrolic structures (M-biliverdenates) are unstable under catalytic hydrogenation conditions (Subramanian and Fuhrhop, 1978). The ease of this sequence with Ni-etioporphyrin (Ni-etio) is apparent by the lack of stable metal intermediates other than the chlorin (M-PH2). 

One of the earliest reported preparations of the requisite glycosidation precursor 5-deoxy-l,2,3-tri-0-acetyl-p-D-ribofuranoside (17) was published by Kissman and Baker in 1957.23 D-Ribose was heated at reflux in a methanol/acetone mixture in the presence of concentrated HCI to provide methyl 2,3-O-isopropylidene-D-ribofuranosidc (21), which was in turn converted to the corresponding 5-O-mesyl ribofuranoside 22 with methanesulfonyl chloride in pyridine in 63% yield. The sulfonate moiety of 22 was then displaced with sodium iodide in refluxing DMF to provide 5-deoxy-5-iodo derivative 23 in 76% yield on a multigram scale. Reductive dehalogenation of 23 was accomplished under heterogeneous catalytic hydrogenation conditions to provide the reduced 2,3-0-protected intermediate 24 in 56% yield, which was subjected to hydrolysis conditions in... 

Schmidt and coworkers [80] developed the pentafluorophenyl ester method for synthesizing cyclopeptides, particularly applicable for 13- and 14-membered ansa peptides. This procedure is superior to the p-nitrophenyl ester method in respect to short reaction time and easy separation of products. Evans and Ellman [81] applied this method to the synthesis of the cyclic tripeptide K-13 146). As shown in Scheme 48, the reaction of the linear precursor 143 with pentafluorophenol and DCC afforded pentafluorophenyl ester 144 in 87-93% yield. Then, under catalytic hydrogenation condition in the presence of a mild base and ethanol, 144 was cyclized to 145 in up to 70% yield. There are more applications of the pentafluorophenyl ester procedure in recent literature [82]. 

Under catalytic hydrogenation conditions, the adducts of nitrones and acrylates, 5-alkoxycarbonyl and 5-aminocarbo-nyl isoxazolidines, give 3-hydroxypyrrolidin-2-ones by intramolecular N-acylation of the amino group. 3,5-Dicarboxylic... 

When 111a is treated with CO or Ce(IV)salts, cleavage of the PRj group takes place with almost quantitative formation of the thiophene derivative 112 (Scheme 39). Under catalytic hydrogenation conditions with Raney nickel, ring contraction via selective sulfur extrusion to the bicy-clo[2.1.1]hexene 113 occurs. - ... 

The total synthesis of the lichen diphenyl ether epiphorellic acid 1 was achieved in the laboratory of J.A. Elix using the Smiles rearrangement as the key step. The diaryl phenolic ester substrate was heated in dry DMSO in the presence of potassium carbonate, which brought about the rearrangement. The resulting carboxylic acid was converted to the methyl ester with diazomethane and was debenzylated under catalytic hydrogenation conditions. 

The enantioselective total synthesis of (-)-hemiasterlin, a marine tripeptide with cytotoxic and antimitotic activity, was achieved by E. Vedejs and co-workers. The asymmetric Strecker reaction was used to construct the key tetramethyltryptophan subunit. The aldehyde substrate was first converted to the corresponding chiral imine with (R)-2-phenylglycinol under scandium triflate catalysis. The addition of tributyltin cyanide resulted in the formation of a-amino nitriles as an 8 1 mixture of diastereomers. Subsequently the cyano group was converted to a primary amide, and the chiral auxiliary was removed under catalytic hydrogenation conditions. 

The preparation of the C1-C21 subunit of the protein phosphatase inhibitor tautomycin was completed by J.A. Marshall et al., and it constituted a formal total synthesis of the natural product. The spiroketal carbon of the target was introduced by the Weinreb ketone synthesis between a lithioalkyne and A/-methoxy-A/-methylurea (a carbon monoxide equivalent). The triple bond of the resulting Weinreb s amide was first reduced under catalytic hydrogenation conditions to yield the corresponding saturated amide, which was reacted with another lithium acetylide to afford an ynone. 

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