A `sugar-coated' carbene precursor: a single crystal X-ray diraction and NMR study y Michael M. Bobek, a Gerald Giester, b Hanspeter KaÈhlig a and Udo H. Brinker a, * a Institut fu Èr Organische Chemie, Universita Èt Wien Wa Èhringer Str. 38, A-1090, Wien, Austria b Institut fu Èr Mineralogie und Kristallographie, Universita Èt Wien, Althanstr. 14, A-1090 Wien, Austria Received 17 May 2000; accepted 8 June 2000 Abstract For the ®rst time, the inclusion complex of any diazirine with a cyclodextrin was studied by single crystal X-ray diraction. This and 2D NMR spectroscopy were employed to elucidate the structure in both the solid state and solution. An opposite orientation of the guest inside the host molecule was revealed. Moreover, crystallization of the neat guest enabled the ®rst X-ray diraction of a dialkyl-substituted dia- zirine. # 2000 Published by Elsevier Science Ltd. Solid state reactions within crystals or con®ned spaces often dier remarkably from corresponding reactions in solution by surpassing them in selectivity, yield, and ease of workup. 1 It has been shown lately, that upon inclusion of diazirines into cyclodextrins the chiroptical properties of an inherently achiral carbene precursor 2 as well as its reactivity can be altered dramatically. 3 Furthermore, it has been demonstrated in a model system that it is feasible to exploit the encapsulation of a diazirine by generating carbenes that react chemospeci®cally to monofunctionalize cyclodextrin hosts in the solid state 4 and in solution. 4,5 Monofunctionalized cyclodextrins possess interesting properties for chiral discrimination and as enzyme mimics. 6 To understand and control the selectivity of photochemical reactions and to further develop selective systems, intimate knowledge of the arrangement and structure of the supramolecular aggregates has to be obtained. Toward this end, the structure of 2-azi-5-hydroxyadamantane 7 (1) and its inclusion complex (1@7-Cy) with b-cyclodextrin (7-Cy) have been studied in the crystal state as well as in aqueous solution. To our knowledge, only four diazirines have been examined by single crystal X-ray diraction analysis. 8 These diazirines, however, bear either a heteroatom or an aromatic moiety attached to the three-membered ring and, therefore, do not re¯ect accurately the structural and electronic properties of the adamantyl system. Though the parent 2-aziadamantane 0040-4039/00/$ - see front matter # 2000 Published by Elsevier Science Ltd. PII: S0040-4039(00)00938-2 Tetrahedron Letters 41 (2000) 5663±5667 * Corresponding author. Fax: +43-1-4277-52140; e-mail: udo.brinker@univie.ac.at y Dedicated to our colleague Dr. Andreas Werner, who was killed in a motorcycle accident.