tert-Butyl 4-(2-diazo­acet­yl)piperazine-1-carboxyl­ate

Åsmund Kaupang; Carl Henrik Görbitz; Tore Hansen

doi:10.1107/S1600536810016211

. 2010 May 8;66(Pt 6):o1299. doi: 10.1107/S1600536810016211

tert-Butyl 4-(2-diazoacetyl)piperazine-1-carboxylate

Åsmund Kaupang ^a, Carl Henrik Görbitz ^a,^*, Tore Hansen ^a

PMCID: PMC2979480 PMID: 21579396

Abstract

The title crystal structure, C₁₁H₁₈N₄O₃, is the first diazoacetamide in which the diazoacetyl group is attached to an N atom. The piperazine ring is in a chair form and hence the molecule has an extended conformation. Both ring N atoms are bonded in an essentially planar configuration with the sum of the C—N—C angles being 359.8 (2) and 357.7 (2)°. In the crystal structure, the O atom of the diazoacetyl group accepts two H atoms from C—H donors, thus generating chains of weak hydrogen-bonded R ₂ ¹(7) rings.

Related literature

For the only other reported synthesis of a diazoacetamide in the Chemical Abstracts Service (CAS, American Chemical Society, 2008 ▶) with a 1,4-diaza six-membered ring, see: Mickelson et al. (1996 ▶). For other diazoacetamides, see: Ouihia et al. (1993 ▶). For related structures, see: Fenlon et al. (2007 ▶); Wang et al. (2006 ▶); Miller et al. (1991 ▶). For synthetic details, see: Kaupang (2010 ▶); Toma et al. (2007 ▶). For hydrogen-bond graph-set notation, see: Bernstein et al. (1995 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

C₁₁H₁₈N₄O₃
M _r = 254.29
Monoclinic,
a = 14.654 (10) Å
b = 10.548 (7) Å
c = 8.553 (6) Å
β = 91.122 (6)°
V = 1321.8 (15) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 105 K
0.55 × 0.42 × 0.08 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.870, T _max = 0.992
7308 measured reflections
2692 independent reflections
2111 reflections with I > 2σ(I)
R _int = 0.041

Refinement

R[F ² > 2σ(F ²)] = 0.038
wR(F ²) = 0.103
S = 1.03
2692 reflections
169 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.17 e Å⁻³
Δρ_min = −0.23 e Å⁻³

Data collection: APEX2 (Bruker, 2007 ▶); cell refinement: SAINT-Plus (Bruker, 2007 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810016211/lh5033sup1.cif

e-66-o1299-sup1.cif^{(17KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810016211/lh5033Isup2.hkl

e-66-o1299-Isup2.hkl^{(132.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1⋯O1ⁱ	0.946 (17)	2.313 (18)	3.250 (3)	170.6 (14)
C3—H32⋯O1ⁱ	0.99	2.36	3.327 (3)	164

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Symmetry code: (i) Inline graphic .

supplementary crystallographic information

Comment

The tert-butyl 4-(2-diazoacetyl)piperazine-1-carboxylate (I) was prepared as part of a series of diazoacetamides, to be used in intramolecular C—H insertion reactions (Kaupang, 2010). It was synthesized from tert-butyl 4-(2-bromoacetyl)piperazine-1-carboxylate by a slight modification of the procedure reported by Toma et al. (2007), employing 1,1,3,3-tetramethylguanidine as the base instead of 1,8-diazabicyclo[5.4.0]undec-7-ene.

Diffraction data were first collected at ambient temperature, yielding a structure with a massively disordered six-membered ring. At 105 K the ring is completely ordered in a well defined chair conformation, Fig. 1.

The diazoacetyl moiety is not an uncommon functional group in organic molecules, however only 15 occurrences were found in the Cambridge Structural Database (Version 5.31 of November 2009; Allen, 2002), and none where, as here, the group is attached to a N atom. In only two structures the group sits on a non-aromatic ring (Miller et al., 1991; Fenlon et al., 2007).

In a model molecule like trimethylamine the N atom is located about 0.45 Å above the plane defined by the three C atoms. In the structure of (I) N3 is 0.125 (2) Å above the plane defined by C2, C3 and C4, while N4 is only 0.039 (2) Å above the plane defined by C5, C6 and C7, which essentially shows a planar configuration (sum of C—N—C angles 359.8 (2) °). This is due to the double bond character of the amidic N3—C2 and N4—C7 bonds measuring 1.3515 (18) and 1.3483 (18) Å, respectively. An example of a related structure is 1,4-di(chloroacetyl)piperazine (Wang et al., 2006).

In the crystal structure, the O atom of the diazoacetyl group accepts two H atoms from C—H donors, thus generating chains of hydrogen-bonded R¹₂(7) rings (Bernstein et al., 1995).

Experimental

A 2.5 ml vial containing tert-butyl 4-(2-diazoacetyl)piperazine-1-carboxylate (10.8 mg) and dichloromethane (1000 ml) was capped and a pinhole (0.5 mm) was made in the cap to allow for vapour diffusion of solvents. This vial was placed inside a 25 ml vial containing n-pentane (8 ml) that was subsequently capped and stored in the dark at ambient temperature for approximately 48 hours, affording bright yellow plate-shaped crystals.