Mono-O-protonated carbamic acid, mono-O-protonated N-methyl carbamate, and mono-O-protonated methyl carbamate and di-O-protonated N,N-bis(carboxyl)-1,2-diaminoethane were prepared in FSO 3 H/SO 2 ClF and FSO 3 H:SbF 5 /SO 2 ClF at -78 °C and were characterized by 1 H, 13 C, and 15 N NMR spectroscopy. Persistent diprotonated carbamic acid, diprotonated N-methyl carbamate, and diprotonated methyl carbamate were not observed under these conditions. The structures, energies, and 13 C and 15 N NMR chemical shifts of mono-, and diprotonated carbamic acids as well as other protonated species were also calculated by ab initio/IGLO/GIAO-MP2 method and compared with the experimental results.

No abstract

No abstract

High‐pressure‐induced inverse‐electron‐demand hetero‐Diels−Alder reactions of ethyl trans‐4‐ethoxy‐2‐oxo‐3‐butenoate (2a) and methyl trans‐4‐benzyloxy‐2‐oxo‐3‐butenoate (2b) with benzyl (cyclopropylidenemethyl) ether (1) each yielded mixtures of two separable diastereomeric esters 7a (64%) and 7b (80%) which, in three subsequent steps, led to the 3‐ethylated and 3‐benzylated α‐ and β‐anomeric benzyl spiro[2‐deoxy‐(D,L)‐arabino‐hexopyranoside‐2,1′‐cyclopropanes] α‐10a,b and β‐10a,b, respectively. The relative configuration of β‐10a was proved by an X‐ray crystal structure analysis. Deprotection of β‐10b was achieved by Pd‐catalyzed hydrogenation in dimethylacetamide leading to spiro[2‐deoxy‐α/β‐2‐(D,L)‐arabino‐hexopyranoside‐2,1′‐cyclopropane] (4). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Previously difficult to prepare, aliphatic and alicyclic trifluoromethylketones (e.g. 1 and 2), which are of pharmacalogic interest as potential enzyme inhibitors, can now be synthesized easily and efficiently. The one-step reaction starting with carbonic esters and trimethyl(trifluoromethyl)silane is induced by tetrabutylammonium fluoride in nonpolar, aprotic solvents and proceeds without formation of double-addition products.