2-tert-Butyl­oxy­methyl-6-cyano-2,3-di­hydro-5H-oxazolo­[3,2-a]­pyrimidin-5-one

The condensation reaction of 2-amino-5-tert-butyl­oxy­methyl-2-oxazoline with ethyl cyano­(ethoxy­methyl­ene)­acetate led to the title cycloadduct. The structure indicates a delocalization in the pyrimidine ring.

S1. Comment

2-Amino-2-oxazolines are found useful synthons for the preparation of various pyrimidine derivatives (Kampe, 1974; Forfar et al., 1990; Chaimbault et al., 1999). As an example, 5-tert-butyloxymethyl-2-amino-2-oxazoline reacted with ethyl cyano(ethoxymethylene)acetate (EMCA) to yield 2-tert-butyloxymethyl-6-cyano-2,3-dihydro-5H-oxazolo[3,2-a]pyrimidin-5-one, (I). Its structure was established by X-ray crystallography. The analysis of bond lengths and angles indicated a π delocalization on the pyrimidine cycle. The fused rings are found almost coplanar. The orientation of the tert-butyloxymethyl chain is defined by the torsion angle C6—O7—C8—C9 = −140.8 (3)°. The crystalline cohesion is ensured by intermolecular van der Waals contacts.

S2. Experimental

Ethyl cyano(ethoxymethylene)acetate (50 mmol) is added dropwise to a solution of 2-amino-5-tert-butyloxymethyl-1,3-oxazoline (50 mmol) in ethanol (150 ml). The solution is stirred magnetically at room temperature overnight. The solvent is evaporated under reduced pressure and the product is recrystallized from tetrachloroethylene (77%). Colourless crystals were grown in ethanol and had m.p. = 375 K.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: Nonius (unpublished); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993).

6-Cyano-2,3-dihydro-2-(tertiobutyloxy)methyl-5H-oxazolo[3,2-a]pyrimidin-5-one,

Crystal data

C12H15N3O3	Dx = 1.312 Mg m^−3
Mr = 249.27	Melting point: 375 K
Monoclinic, P21/c	Cu Kα radiation, λ = 1.54178 Å
a = 11.903 (1) Å	Cell parameters from 25 reflections
b = 10.895 (2) Å	θ = 4.0–64.9°
c = 10.343 (1) Å	µ = 0.80 mm^−1
β = 109.76 (1)°	T = 296 K
V = 1262.3 (3) Å^3	Plate, colourless
Z = 4	0.25 × 0.25 × 0.02 mm
F(000) = 528

Data collection

Enraf Nonius CAD-4 diffractometer	1243 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	θmax = 64.9°, θmin = 4.0°
Graphite monochromator	h = 0→13
ω–2θ scans	k = 0→12
Absorption correction: ψ scan (north et al., 1968) ?	l = −12→11
Tmin = 0.854, Tmax = 0.999	2 standard reflections every 90 reflections
2060 measured reflections	intensity decay: none
2060 independent reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.057	H-atom parameters not refined
wR(F^2) = 0.131	Calculated w = 1/[σ^2(Fo^2) + (0.0738P)^2 + 0.5706P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
2059 reflections	Δρmax = 0.24 e Å^−3
164 parameters	Δρmin = −0.17 e Å^−3
0 restraints	Extinction correction: SHELXL93, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0023 (5)

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 on F² for ALL reflections except for 1 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating _R_factor_obs 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
C3	−0.0128 (5)	0.6303 (5)	0.0997 (5)	0.123 (2)
H3A	0.0431 (5)	0.6520 (5)	0.0548 (5)	0.184*
H3B	−0.0705 (5)	0.6948 (5)	0.0869 (5)	0.184*
H3C	−0.0527 (5)	0.5556 (5)	0.0610 (5)	0.184*
C4	0.1207 (4)	0.7259 (4)	0.3126 (5)	0.110 (2)
H4A	0.1744 (4)	0.7470 (4)	0.2647 (5)	0.166*
H4B	0.1654 (4)	0.7110 (4)	0.4076 (5)	0.166*
H4C	0.0659 (4)	0.7923 (4)	0.3055 (5)	0.166*
C5	−0.0316 (4)	0.5784 (5)	0.3237 (6)	0.115 (2)
H5A	0.0122 (4)	0.5676 (5)	0.4197 (6)	0.173*
H5B	−0.0715 (4)	0.5033 (5)	0.2864 (6)	0.173*
H5C	−0.0895 (4)	0.6425 (5)	0.3123 (6)	0.173*
C6	0.0526 (3)	0.6125 (3)	0.2503 (4)	0.0611 (9)
O7	0.1342 (2)	0.5127 (2)	0.2540 (2)	0.0643 (7)
C8	0.2074 (3)	0.4702 (3)	0.3847 (4)	0.0650 (9)
H8A	0.1730 (3)	0.3968 (3)	0.4093 (4)	0.078*
H8B	0.2133 (3)	0.5324 (3)	0.4537 (4)	0.078*
C9	0.3293 (3)	0.4421 (3)	0.3783 (3)	0.0598 (9)
H9	0.3797 (3)	0.4058 (3)	0.4652 (3)	0.072*
O10	0.3809 (2)	0.5589 (2)	0.3545 (2)	0.0624 (6)
C11	0.3744 (2)	0.5623 (3)	0.2240 (3)	0.0513 (8)
N12	0.3453 (2)	0.4529 (2)	0.1627 (3)	0.0466 (6)
C13	0.3304 (3)	0.3615 (3)	0.2582 (4)	0.0620 (9)
H13A	0.3963 (3)	0.3039 (3)	0.2853 (4)	0.074*
H13B	0.2560 (3)	0.3169 (3)	0.2195 (4)	0.074*
N14	0.3970 (2)	0.6628 (2)	0.1692 (3)	0.0623 (8)
C15	0.3884 (3)	0.6487 (3)	0.0359 (4)	0.0602 (9)
H15	0.4023 (3)	0.7173 (3)	−0.0100 (4)	0.072*
C16	0.3610 (2)	0.5415 (3)	−0.0355 (3)	0.0523 (8)
C17	0.3407 (2)	0.4319 (3)	0.0295 (3)	0.0508 (8)
C18	0.3575 (3)	0.5337 (3)	−0.1747 (4)	0.0645 (10)
N19	0.3562 (3)	0.5258 (3)	−0.2858 (4)	0.0903 (11)
O20	0.3220 (2)	0.3287 (2)	−0.0200 (2)	0.0678 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C3	0.107 (4)	0.144 (5)	0.097 (4)	0.066 (4)	0.006 (3)	0.005 (3)
C4	0.099 (3)	0.068 (3)	0.152 (4)	−0.014 (2)	0.027 (3)	−0.017 (3)
C5	0.086 (3)	0.097 (3)	0.189 (5)	0.009 (3)	0.080 (3)	0.010 (3)
C6	0.051 (2)	0.055 (2)	0.077 (2)	−0.001 (2)	0.021 (2)	−0.006 (2)
O7	0.0537 (12)	0.076 (2)	0.0570 (14)	0.0135 (11)	0.0109 (10)	−0.0027 (12)
C8	0.065 (2)	0.072 (2)	0.058 (2)	0.002 (2)	0.022 (2)	0.009 (2)
C9	0.055 (2)	0.062 (2)	0.055 (2)	0.005 (2)	0.010 (2)	0.005 (2)
O10	0.0569 (13)	0.062 (2)	0.063 (2)	−0.0054 (11)	0.0119 (11)	−0.0092 (12)
C11	0.038 (2)	0.047 (2)	0.062 (2)	0.0006 (14)	0.0079 (14)	−0.005 (2)
N12	0.0414 (13)	0.040 (2)	0.055 (2)	0.0001 (11)	0.0116 (11)	−0.0004 (12)
C13	0.059 (2)	0.054 (2)	0.072 (2)	0.003 (2)	0.021 (2)	0.008 (2)
N14	0.057 (2)	0.045 (2)	0.081 (2)	−0.0073 (13)	0.0188 (15)	−0.0053 (15)
C15	0.044 (2)	0.051 (2)	0.079 (3)	−0.0006 (14)	0.013 (2)	0.011 (2)
C16	0.037 (2)	0.053 (2)	0.063 (2)	0.0037 (14)	0.0112 (14)	0.006 (2)
C17	0.0349 (14)	0.049 (2)	0.064 (2)	0.0010 (13)	0.0105 (13)	−0.003 (2)
C18	0.047 (2)	0.072 (3)	0.069 (3)	0.006 (2)	0.013 (2)	0.010 (2)
N19	0.085 (2)	0.111 (3)	0.071 (2)	0.008 (2)	0.021 (2)	0.009 (2)
O20	0.0700 (15)	0.055 (2)	0.075 (2)	−0.0024 (12)	0.0202 (12)	−0.0120 (13)

Geometric parameters (Å, º)

C3—C6	1.500 (5)	C11—N12	1.340 (4)
C4—C6	1.498 (5)	N12—C17	1.379 (4)
C5—C6	1.494 (5)	N12—C13	1.456 (4)
C6—O7	1.450 (4)	N14—C15	1.356 (4)
O7—C8	1.416 (4)	C15—C16	1.362 (4)
C8—C9	1.506 (5)	C16—C18	1.429 (5)
C9—O10	1.469 (4)	C16—C17	1.431 (4)
C9—C13	1.525 (5)	C17—O20	1.224 (4)
O10—C11	1.326 (4)	C18—N19	1.147 (4)
C11—N14	1.302 (4)
O7—C6—C5	111.0 (3)	O10—C11—N12	112.0 (3)
O7—C6—C3	103.4 (3)	C11—N12—C17	122.6 (3)
C5—C6—C3	111.0 (4)	C11—N12—C13	111.0 (3)
O7—C6—C4	110.3 (3)	C17—N12—C13	126.3 (3)
C5—C6—C4	110.2 (4)	N12—C13—C9	101.3 (3)
C3—C6—C4	110.8 (4)	C11—N14—C15	113.1 (3)
C8—O7—C6	117.4 (3)	N14—C15—C16	124.8 (3)
O7—C8—C9	108.4 (3)	C15—C16—C18	121.2 (3)
O10—C9—C8	107.2 (3)	C15—C16—C17	120.6 (3)
O10—C9—C13	104.1 (3)	C18—C16—C17	118.2 (3)
C8—C9—C13	115.2 (3)	O20—C17—N12	120.7 (3)
C11—O10—C9	108.1 (2)	O20—C17—C16	127.3 (3)
N14—C11—O10	121.1 (3)	N12—C17—C16	112.0 (3)
N14—C11—N12	126.9 (3)	N19—C18—C16	178.8 (4)
C5—C6—O7—C8	−58.7 (4)	O10—C9—C13—N12	−17.5 (3)
C3—C6—O7—C8	−177.8 (3)	C8—C9—C13—N12	99.6 (3)
C4—C6—O7—C8	63.7 (4)	O10—C11—N14—C15	178.7 (3)
C6—O7—C8—C9	−140.8 (3)	N12—C11—N14—C15	0.1 (4)
O7—C8—C9—O10	65.3 (3)	C11—N14—C15—C16	−0.9 (4)
O7—C8—C9—C13	−50.0 (4)	N14—C15—C16—C18	−178.0 (3)
C8—C9—O10—C11	−104.1 (3)	N14—C15—C16—C17	−1.1 (5)
C13—C9—O10—C11	18.4 (3)	C11—N12—C17—O20	174.8 (3)
C9—O10—C11—N14	169.5 (3)	C13—N12—C17—O20	0.4 (4)
C9—O10—C11—N12	−11.8 (3)	C11—N12—C17—C16	−4.6 (4)
N14—C11—N12—C17	3.0 (4)	C13—N12—C17—C16	−179.0 (2)
O10—C11—N12—C17	−175.7 (2)	C15—C16—C17—O20	−175.6 (3)
N14—C11—N12—C13	178.2 (3)	C18—C16—C17—O20	1.4 (4)
O10—C11—N12—C13	−0.5 (3)	C15—C16—C17—N12	3.7 (4)
C11—N12—C13—C9	11.7 (3)	C18—C16—C17—N12	−179.3 (3)
C17—N12—C13—C9	−173.3 (3)