Crystal structure of (±)-(5SR,6SR)-6-ethenyl-1-[(RS)-1-phenylethoxy]-1-azaspiro[4.5]decan-2-one

In the title compound, the pyrrolidine and cyclohexane rings exhibit envelope and chair conformations, respectively. In the crystal, C—H⋯O interactions connect the molecules into tape structures.

In the title compound, C 19 H 25 NO 2 , the pyrrolidine ring adopts an envelope form, with the spiro C atom as the flap, while the cyclohexane ring shows a chair form. A weak intramolecular C-HÁ Á ÁO interaction supports the molecular conformation, generating an S(6) ring motif. In the crystal, pairs of C-HÁ Á ÁO interactions connect the molecules into inversion dimers with an R 2 2 (16) ring motif. The dimers are linked by a second pair of C-HÁ Á ÁO interactions, enclosing an R 4 2 (12) ring motif, into a tape structure along the b axis.

Chemical context
A number of compounds containing an N-hydroxy or N-alkoxy substituent have been widely explored in organic synthesis. These substances show specific and intriguing reactivity caused by a covalent bond between the electronegative heteroatoms. Among these compounds, for example, the N-alkoxyamines are known to be initiators for stable free radical polymerization (Hawker et al., 2001), and the N-alkoxyamides are utilized for mild and effective acylating agents (cf. Weinreb amide; Nahm & Weinreb, 1981). We noticed this stable but contributable functionality, and have developed a new synthetic pathway to synthesize the natural alkaloids (Sato & Chida, 2014).
The structure of an N-methoxy-azaspirocyclic derivative, (d), which is related to the title compound, (e), has also been reported (TUWCUJ; Wardrop et al., 2003). In the crystal of (d), the pyrrolidine ring adopts a similar conformation to the title compound. The spiro-C atom is at the flap of the envelope, and the geometry around the N atom shows a little The molecular structure of the title compound, showing the the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. The black dashed line indicates the intramolecular C-HÁ Á ÁO hydrogen bond. Only H atoms connected to chiral C atoms are shown for clarity. Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx; Ày; Àz þ 1; (ii) x; y À 1; z.

Figure 2
A partial packing view showing the tape structure. Black dashed lines indicate the intermolecular C-HÁ Á ÁO hydrogen bonds. Only H atoms involved in the hydrogen bonds are shown for clarity. [Symmetry codes:

Synthesis and crystallization
The title compound was synthesized convergently from hex-5en-1-ol, methyl 4-chloro-4-oxobutyrate and 1-phenylethanol (Yamamoto et al., 2015). Purification was carried out by silica gel column chromatography, and colorless crystals were obtained from a hexane solution by slow evaporation at ambient temperature. M.p. 357.

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Acta Cryst. program(s) used to solve structure: SHELXS2013 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2010) and PLATON (Spek, 2009).  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. Problematic one reflection with |I(obs)-I(calc)|/σW(I) greater than 10 (5 4 0) has been omitted in the final refinement.