The chemistry of reactive intermediates (guests) within the confined spaces of another species (host) presents interesting opportunities for the discovery of new reactions."] The reactive behavior of carbenes in constrained systems is expected to be very different from that of free carbenes in solution or in the gas phase. The "tight fit" between the structures of hosts and the guest carbenes should alter both inter-and intramolecular reactions. Furthermore, suitable cavity sizes will restrict the mobility of the entrapped carbenes, which are then anticipated to react more selectively.Carbene chemistry in different media has been studied extensively over the past decades.121 Nearly nothing, however, is known about carbenes generated in constrained systems. Although x-and fi-cyclodextrin (CD) have been the only molecules employed as hosts,[31 the intermediacy of carbenes or the corresponding carbenoids has not been firmly e~t a b l i s h e d .~~]The relatively stabler4] diazirine I derived from adamantaneIsl was chosen as the guest-carbene precursor and fi-CD as the molecular reaction vessel (see Scheme 1). Compound 1 was prepared according to the literature,['] purified by column chromatography (silica gel) under the exclusion of light, and shown to be pure by ' H N M R spectroscopy.The / K D complex of 1 (1 . p-CD) was synthesized (ratio of host: guest ca. 3: 1) and characterized. To avoid the replacement of entrapped guest molecules in the fi-CD cavity by solvent molecules, solid-state NMR spectroscopy was used for the characterization. Cross polarization/magic angle spinning (CP/MAS) 13C N M R spectra provide convincing evidence that an inclusion complex was formed.['] This is further supported by powder X-ray diffraction spectra of 1, P-CD, 1 P-CD, and a physical mixture of 1 and a-CD.Under the conditions of fast atom bombardment (FAB) mass spectrometry, however, the loosely bound complex does not survive, and only the (M -H)-peak of 8-CD is observed.I8]In addition, molecular modeling was used to gain information about the fit and possible position of 1 within the C D cavity.'" According to calculations carried out by using the SYBYL force field with default parameters, 1 is nearly completely submerged into the fl-CD cavity with the diazirine function at the wider rim of the truncated cone.
Die ersten intra‐ und intermolekularen Carbeninsertionen in einem räumlich begrenzten molekularen Reaktionsgefäß konnten bei der Photolyse des festen Einschlußkomplexes 1·β‐Cyclodextrin(CD) nachgewiesen werden. NMR‐spektroskopische und/oder massenspektrometrische Untersuchungen belegen die Bildung von Produkten wie 2·β‐CD und 3·β‐CD.
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