Carbenes, ethoxy carbonyl

Thus for instance, in the sensitization experiments carried out with ethoxy-carbonyl-carbene, dimethoxy-carbonylcarbene, and carbene A, the light capture was generally more than 80% 35> Jn the case of phenyl-cyclopentadienyhdenes the nonstereospecificity clearly depends on the fight capture by the sensitizer... 

In the sensitized generation of ethoxy-carbonyl-carbene the fight capture by the diazocompound is only 25% A number of photosensitized reactions of triplet carbenes with cis- and trans-olefins are fisted in Table 10. The sensitizers used, as well as their various triplet energies Et, are also given in the table. 

Dioxol 2,2-Dimethyl-4-ethoxy-carbonyl- E19b, 1316 (Carben-... 

Heptadiensaure 6-Acetoxy-2-methyl- IV/5b, 752 f. 2,4-Hexadiendisaure 2,5-Dimethyl- -dimethylester V/lc, 680 3-Oxa-bicyclo[3.i.O hexan 1-Ethoxy-carbonyl-6,6-dimethyl-2-oxo-E19b, 1089 [(Carben + En (intra)J... 

Cyclopropan 2,2-Dimethyl-l-ethoxy-carbonyl-1 -trimethy lgermy 1-E19b, 1453 (Carben + En)... 

Whether a cyclopropanation reaction is stereospecific or not, is often tested with (Z)- and ( )-but-2-ene, but of course, this problem also holds for other diastereomeric alkenes. The following carbenes, generated by direct irradiation of the corresponding a-diazocarbonyl compound, undergo stereo specific or highly stereoselective cycloaddition to (Z)- and ( )-but-2-ene methoxycarbonylcarbene,105-106 chloro-, bromo- and iodo(ethoxycarbonyl)carbene,107 eth-oxycarbonyl(trimethylsilyl)carbene,108 ethoxycarbonyl(trimethylgermyl)carbene,109 ethoxy-carbonyl(trimethylstannyl)carbene,109 ethoxycarbonyl(trimethylplumbyl)carbene,109 ethoxy-carbonyl trimethylmercuriojcarbene.1 10... 

Dotz and coworkers prepared several interesting and novel glycosylidene carbenes (259-261) by reaction of lithiated glycal 258 with the appropriate metal carbonyl derivative. The synthetic utility of the formed carbenes was demonstrated by reaction with 3-hexyne to give a mixture of complexed and uncomplexed adducts 262 and 263, respectively. The anomeric chromium carhene 264 was converted to 265 hy exposure to ethoxy ethyne (Scheme 48) [70]. The same workers have carried out a similar chromium-mediated henzannulation (266 —> 268), this time with the chromium on the aromatic fragment [71]. Other sugar-hased carhenes have also been prepared [72]. 

Ducept and Marsden described a general synthesis of 5-ethoxy-2-substituted 4-(triethylsilyl)oxazoles 176 from the rhodium(II)octanoate-catalyzed diazo-transfer reaction of ethyl (triethylsilyl)diazoacetate 175 and nitriles (Scheme 1.48). The reaction conditions tolerate a wide variety of functional groups on the nitrile, including alkyl, aryl, heteroaryl, vinyl, carbonyl, sUyloxy, and dialkylamino. Desilylation of 176 with TBAF afforded the corresponding 2-alkyl(aryl)-5-ethoxy-oxazoles 177, which are normally inaccessible from diazoesters using conventional rhodium-carbene methodology. The authors noted that carbonyl groups in the 2 position of 176 are not compatible with TBAF deprotection. 

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