Cyclopentanones crystal structure

Fig. 7.3. Crystal structures of some lithium etiolates of ketones. (A) Unsolvated hexameric enolate of methyl t-butyl ketone (B) tetrahydrofuran solvate of tetramer of enolate of methyl r-butyl ketone (C) tetrahydrofuran solvate of tetramer of enolate of cyclopentanone (D) dimeric enolate of 3,3-dimethyl-4-(r-butyldimethylsiloxy)-2-pentanone. (Structural diagrams are reproduced from Refs. 66-69.) by permission of the American Chemical Society and Verlag Helvetica Chimica Acta AG.

Seebach, Dunitz and coworkers reported, in 1981226, the first crystal structures of lithium enolates of simple ketones, obtained in THF from pinacolone (3,3-dimethyl-2-butanone) and cyclopentanone. Both were arranged as tetrasolvated cubic tetramers, one THF molecule capping each lithium cation (Scheme 58A). Note that pinacolone enolate can also be crystallized, from heptane at — 20 °C, as a prismatic unsolvated hexamer exhibiting an approximate S6 symmetry and six slight it-cation interactions227,228 (Scheme 58B) or as a dimer in the presence of 2 molecules of TriMEDA29. Similarly,... 

Exactly 10 years after the previous statement appeared, the first lithium enolate crystal structures were published as (5) and (6). Thus, structural information derived from X-ray diffraction analysis proved the tetrameric, cubic geometry for the THF-solvated, lithium enolates derived from r-butyl methyl ketone (pinacolone) and from cyclopentanone. Hence, the tetrameric aggregate characterized previously by NMR as (7) was now defined unambiguously. Moreover, the general tetrameric aggregate (7) now became embellished in (5) and (6) by the inclusion of coordinating solvent molecules, i.e. THE. A representative quotation from this 1981 crystal structure analysis is given below. 

The same tetracyclization mode is observed for any 2-halodienyne in which the two tethers between the 2-haloethenyl starter and the alkynyl relay as well as between the latter and the terminal double bond are four or more atoms long, even when the alkenyl terminator is not substituted in the 2-position (Scheme 33, Eqs. 1 and 2). Thus, a cyclopentanone derivative fitted with a 3-ethenyl and a 2-(8 -bromo-2 -oxonon- 8 -en-3 -ynyl) tether did not cyclize to the tetracyclic steroid skeleton, but to the pentacycle with a five-membered B-ring and a bridging cyclopropane moiety, as was proved by an X-ray crystal structure analysis of the cw-diastereomer (Scheme 33, Eq. 3). ... 

The absolute configuration (S) of the stereocentre was assigned based on comparison of the optical rotation values of analogous tertiary a-aryl cyclopentanones and cyclohexanones reported in the literature. This was further confirmed by obtaining an X-ray crystal structure of cyclopentanone 7a and cyclohexanone 24b (Fig. 6.1). 

ABSTRACTii Cyci odeKtr i ns open great possi bi 1 i ti es for studying bath th66 crystal structure and the spectroscopic properties, in solution of the same compound In the present paper new inclusion compounds are studied. Two conformati onaly 1abi1e moleculbb (cyclopentanone,... 

Condensation of [3- or "y-amino alcohols with aldehydes or ketones RR CO gives the product 27. In solution the position of the equilibrium varies with R and R, and with the solvent (73). When the carbonyl reactant is a substituted benzaldehyde, the solid is found (IR, KBr) to comprise molecules of the open-chain structure 27a, whereas aliphatic aldehydes and ketones give crystals of dihydro- 1,3-benzoxazines, 27b. An interesting case is that of the condensation product of o-hydroxybenzylamine with cyclopentanone, for which McDonagh and Smith (73) suggest that ring and chain tautomers coexist in the solid. 

Compound 63 has been structurally characterised by single crystal X-ray diffraction (Fig. 21a).52 53 The geometry of the five-membered metallacyclic ring is puckered with notably different Co C( ) distances. The C-C bonds are also observed to be significantly shorter than the standard (sp3)C-(sp3)C bond length. Compound 63 was found to be stable at room temperature under an N2 atmosphere and could be stored for months at —30 °C.67 However, in benzene solution, 63 decomposes at room temperature giving a mixture of 1-butene (11%), trans 2-butene (64%) and cis 2-butene (25%).68 Reaction of 63 with CO at 44 atm pressure afforded cyclopentanone as the product in 33% yield, while reaction with ethylene at 1 atm gave 1-hexene (65%) and 1-butene (11%) as the products.68... 

Figure 8.27 (a) Topotactic, single crystal solid-state photodimerisation of 5-benzyl-2-benzylidene-cyclopentanone. (b) Superposition of the structures of the starting material and dimersied product (reprinted with permission from [33] 1981 American Chemical Society). 

---