tert-Butyl 2-borono-1H-pyrrole-1-carboxyl­ate

In the crystal structure of the title compound, C₉H₁₄BNO₄, the boronic acid group and carbamate groups are nearly co-planar with the pyrrole ring, making dihedral angles of 0.1 (2) and 2.2 (2)°, respectively. Intra­molecular and inter­molecular O—H⋯O hydrogen bonds help to stabilize the structure, the latter interaction leading to inversion dimers..

Related literature

For general background, see: Hall (2005); Kelly & Fuchs (1993).

Experimental

Crystal data

• C₉H₁₄BNO₄

• M_r = 211.02

• Orthorhombic, P b c a

• a = 13.014 (3) Å

• b = 9.940 (2) Å

• c = 17.417 (4) Å

• V = 2252.9 (9) ų

• Z = 8

• Mo Kα radiation

• μ = 0.10 mm⁻¹

• T = 293 K

• 0.25 × 0.12 × 0.10 mm

Data collection

• Bruker SMART 1000 CCD area-detector diffractometer

• Absorption correction: none

• 9542 measured reflections

• 2213 independent reflections

• 1208 reflections with I > 2σ(I)

• R_int = 0.065

Refinement

• R[F² > 2σ(F²)] = 0.042

• wR(F²) = 0.106

• S = 0.85

• 2213 reflections

• 192 parameters

• All H-atom parameters refined

• Δρ_max = 0.12 e Å⁻³

• Δρ_min = −0.21 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3A⋯O2	0.87 (2)	1.73 (2)	2.5819 (18)	164.7 (18)
O4—H4⋯O3^i	0.89 (3)	1.88 (3)	2.769 (3)	173 (3)
Symmetry code: (i) -x+2, -y+1, -z+1.

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; 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.

Supporting information

S1. Comment

Boronic acids are versatile compounds widely used in the synthesis of biaryls, as therapeutical agents, and as chemical sensors (Hall, 2005). The title compound is the key intermediate for the synthesis of (+)-pinanediol-L-boroproline (Kelly & Fuchs, 1993).

In the molecular structure of the title compound (Fig. 1), the pyrrole ring, the boronic acid group and the carboxyl groups are almost co-planar. The carbonyl links with the adjacent boronic acid group via O3—H3···O2 hydrogen bonding. Intermolecular hydrogen bond is also observed in the crystal structure (Table 1).

Related literature

For general background, see: Hall (2005); Kelly & Fuchs (1993).

S2. Experimental

All chemical reagents are commercial and used as received. Under -78°C and argon atmosphere, lithium diisopropylamide (1.0 M in THF, 5.0 ml, 5.0 mmol) was added dropwise to a solution of tert-butyl 1H-pyrrole-1-carboxylate (835 mg, 5.0 mmol) in dry THF (15 ml), and the solution was stirred at this temperature for 30 min. Trimethylborate (1.7 ml, 15 mmol) was added dropwise, and the mixture was allowed to warm to room temperature over 2 h and stirred overnight. After aqueous workup, the crude product was crystallized from hexanes. Single crystals suitable for X-ray analysis were obtained by recrystallization from a mixed solvent of ethyl acetate and hexane at ambient temperature (20–25°C).

S3. Refinement

H atoms were located in a difference Fourier map and refined isotropically.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

Fig. 1. The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are drawn as spheres of arbitrary radii.

Tert-butyl 2-borono-1H-pyrrole-1-carboxylate

Crystal data

C9H14BNO4	F(000) = 896
Mr = 211.02	Dx = 1.244 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 810 reflections
a = 13.014 (3) Å	θ = 2.3–22.4°
b = 9.940 (2) Å	µ = 0.10 mm^−1
c = 17.417 (4) Å	T = 293 K
V = 2252.9 (9) Å^3	Prism, colorless
Z = 8	0.25 × 0.12 × 0.10 mm

Data collection

Bruker SMART 1000 CCD area-detector diffractometer	1208 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.065
Graphite monochromator	θmax = 26.0°, θmin = 2.3°
ϕ and ω scans	h = −16→13
9542 measured reflections	k = −12→12
2213 independent reflections	l = −21→19

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.106	All H-atom parameters refined
S = 0.85	w = 1/[σ^2(Fo^2) + (0.0588P)^2] where P = (Fo^2 + 2Fc^2)/3
2213 reflections	(Δ/σ)max < 0.001
192 parameters	Δρmax = 0.12 e Å^−3
0 restraints	Δρmin = −0.21 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
B1	1.03949 (15)	0.6990 (2)	0.51802 (11)	0.0727 (6)
C1	1.09811 (14)	1.0494 (2)	0.59196 (12)	0.0767 (5)
C2	1.17519 (16)	1.0274 (3)	0.54329 (13)	0.0893 (7)
C3	1.16298 (14)	0.8995 (3)	0.51194 (12)	0.0821 (6)
C4	1.07732 (12)	0.83956 (18)	0.54116 (8)	0.0644 (5)
C5	0.94986 (12)	0.92187 (19)	0.63777 (9)	0.0635 (4)
C6	0.85439 (15)	1.03344 (19)	0.74024 (10)	0.0771 (5)
C7	0.75166 (18)	1.0282 (3)	0.70204 (16)	0.0955 (7)
C8	0.8711 (3)	0.9215 (3)	0.79700 (14)	0.1000 (7)
C9	0.8746 (3)	1.1693 (3)	0.7756 (2)	0.1119 (9)
N1	1.03646 (9)	0.93560 (14)	0.59221 (7)	0.0631 (4)
O1	0.93714 (8)	1.02801 (13)	0.68119 (7)	0.0754 (4)
O2	0.89519 (9)	0.82427 (13)	0.63724 (7)	0.0776 (4)
O3	0.95566 (10)	0.63485 (15)	0.54641 (8)	0.0921 (5)
O4	1.09809 (10)	0.6338 (2)	0.46635 (8)	0.0960 (5)
H3	1.2044 (14)	0.8510 (17)	0.4741 (10)	0.083 (5)*
H7A	0.7006 (17)	1.040 (2)	0.7397 (13)	0.104 (7)*
H7B	0.7430 (18)	1.106 (3)	0.6664 (14)	0.131 (10)*
H8A	0.8247 (16)	0.934 (2)	0.8403 (14)	0.109 (7)*
H1	1.0760 (14)	1.126 (2)	0.6241 (11)	0.089 (6)*
H9A	0.8259 (16)	1.184 (2)	0.8132 (14)	0.122 (8)*
H9B	0.8706 (15)	1.236 (2)	0.7359 (14)	0.109 (9)*
H7C	0.7384 (15)	0.942 (2)	0.6764 (13)	0.104 (7)*
H2	1.2262 (17)	1.090 (2)	0.5323 (11)	0.104 (7)*
H8B	0.941 (2)	0.928 (2)	0.8167 (14)	0.130 (9)*
H9C	0.949 (2)	1.169 (3)	0.7937 (16)	0.169 (12)*
H8C	0.8565 (17)	0.826 (3)	0.7735 (14)	0.135 (9)*
H3A	0.9265 (14)	0.6888 (19)	0.5791 (11)	0.087 (6)*
H4	1.080 (2)	0.548 (3)	0.4581 (16)	0.145 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
B1	0.0572 (11)	0.1046 (17)	0.0563 (11)	0.0146 (11)	−0.0040 (9)	−0.0053 (11)
C1	0.0616 (11)	0.0916 (15)	0.0767 (12)	−0.0077 (11)	−0.0134 (10)	0.0135 (12)
C2	0.0590 (12)	0.120 (2)	0.0888 (15)	−0.0117 (12)	−0.0074 (11)	0.0335 (14)
C3	0.0565 (11)	0.1260 (19)	0.0638 (11)	0.0091 (12)	0.0003 (9)	0.0161 (13)
C4	0.0524 (9)	0.0915 (13)	0.0492 (8)	0.0113 (9)	−0.0034 (7)	0.0069 (9)
C5	0.0586 (10)	0.0744 (12)	0.0576 (9)	0.0032 (9)	−0.0030 (8)	0.0004 (9)
C6	0.0834 (13)	0.0832 (13)	0.0647 (11)	0.0110 (10)	0.0065 (9)	−0.0149 (10)
C7	0.0793 (15)	0.116 (2)	0.0913 (17)	0.0166 (14)	0.0054 (13)	−0.0170 (17)
C8	0.119 (2)	0.115 (2)	0.0655 (13)	0.0172 (16)	0.0126 (14)	0.0019 (14)
C9	0.129 (2)	0.103 (2)	0.103 (2)	0.0076 (16)	0.0117 (18)	−0.0376 (18)
N1	0.0494 (7)	0.0814 (10)	0.0585 (8)	−0.0007 (7)	−0.0031 (6)	0.0075 (7)
O1	0.0787 (8)	0.0766 (8)	0.0708 (7)	−0.0010 (6)	0.0069 (6)	−0.0128 (7)
O2	0.0698 (7)	0.0786 (9)	0.0844 (8)	−0.0067 (6)	0.0214 (6)	−0.0166 (7)
O3	0.0730 (8)	0.1037 (11)	0.0996 (10)	−0.0004 (7)	0.0200 (7)	−0.0384 (8)
O4	0.0799 (9)	0.1217 (14)	0.0863 (9)	0.0147 (8)	0.0190 (7)	−0.0238 (9)

Geometric parameters (Å, º)

B1—O4	1.346 (2)	C6—C7	1.494 (3)
B1—O3	1.357 (2)	C6—C8	1.504 (3)
B1—C4	1.535 (3)	C6—C9	1.507 (3)
C1—C2	1.331 (3)	C7—H7A	0.94 (2)
C1—N1	1.387 (2)	C7—H7B	0.99 (3)
C1—H1	0.99 (2)	C7—H7C	0.98 (2)
C2—C3	1.393 (3)	C8—H8A	0.97 (2)
C2—H2	0.93 (2)	C8—H8B	0.98 (3)
C3—C4	1.363 (3)	C8—H8C	1.05 (3)
C3—H3	0.978 (18)	C9—H9A	0.92 (2)
C4—N1	1.409 (2)	C9—H9B	0.96 (2)
C5—O2	1.2030 (19)	C9—H9C	1.02 (3)
C5—O1	1.309 (2)	O3—H3A	0.87 (2)
C5—N1	1.385 (2)	O4—H4	0.89 (3)
C6—O1	1.490 (2)
O4—B1—O3	118.2 (2)	C6—C7—H7A	108.5 (13)
O4—B1—C4	115.60 (19)	C6—C7—H7B	110.6 (14)
O3—B1—C4	126.14 (17)	H7A—C7—H7B	105.0 (18)
C2—C1—N1	107.7 (2)	C6—C7—H7C	112.9 (12)
C2—C1—H1	135.0 (12)	H7A—C7—H7C	107.4 (18)
N1—C1—H1	117.2 (11)	H7B—C7—H7C	112 (2)
C1—C2—C3	108.3 (2)	C6—C8—H8A	109.2 (12)
C1—C2—H2	123.9 (13)	C6—C8—H8B	108.4 (15)
C3—C2—H2	127.8 (13)	H8A—C8—H8B	107 (2)
C4—C3—C2	110.3 (2)	C6—C8—H8C	112.7 (13)
C4—C3—H3	119.1 (11)	H8A—C8—H8C	107.5 (18)
C2—C3—H3	130.7 (10)	H8B—C8—H8C	111 (2)
C3—C4—N1	104.36 (18)	C6—C9—H9A	107.9 (16)
C3—C4—B1	124.22 (18)	C6—C9—H9B	108.3 (13)
N1—C4—B1	131.40 (15)	H9A—C9—H9B	112 (2)
O2—C5—O1	125.44 (15)	C6—C9—H9C	107.0 (17)
O2—C5—N1	123.79 (16)	H9A—C9—H9C	116 (2)
O1—C5—N1	110.77 (15)	H9B—C9—H9C	106 (2)
O1—C6—C7	109.75 (16)	C5—N1—C1	123.57 (16)
O1—C6—C8	108.80 (16)	C5—N1—C4	127.01 (15)
C7—C6—C8	113.4 (2)	C1—N1—C4	109.41 (16)
O1—C6—C9	100.86 (18)	C5—O1—C6	121.30 (13)
C7—C6—C9	111.6 (2)	B1—O3—H3A	107.4 (12)
C8—C6—C9	111.6 (2)	B1—O4—H4	114.5 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O3^i	0.89 (3)	1.88 (3)	2.769 (3)	173 (3)
O3—H3A···O2	0.87 (2)	1.73 (2)	2.5819 (18)	164.7 (18)

Symmetry code: (i) −x+2, −y+1, −z+1.