tert-Butyl 4-isopropyl-2-oxo-6-phenyl-3,4-dihydro-2H-pyran-3-carboxyl­ate

Wei Chen; Miao Yu; Si Li; Ning Jiao

doi:10.1107/S160053681001367X

. 2010 Apr 17;66(Pt 5):o1103. doi: 10.1107/S160053681001367X

tert-Butyl 4-isopropyl-2-oxo-6-phenyl-3,4-dihydro-2H-pyran-3-carboxylate

Wei Chen ^a, Miao Yu ^b,^*, Si Li ^c, Ning Jiao ^c

PMCID: PMC2979271 PMID: 21579155

Abstract

In the title compound, C₁₉H₂₄O₄, the six-membered lactone ring adopts an envelope conformation with the tert-butoxycarbonyl and isopropyl substituents in axial positions, and the phenyl group in an equatorial position. In the crystal structure, weak intermolecular C—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers.

Related literature

For the applications and synthesis of endocyclic enol lactones, see: Davies & Jin (2004 ▶); Evans et al. (2005 ▶); Krafft & Katzenellenbogen (1981 ▶); Li et al. (2007 ▶); Zeni et al. (2004 ▶); Zhao et al. (1997 ▶); Jimenez-Tenorio et al. (2001 ▶). For the synthesis, see: Li et al. (2009 ▶).

Experimental

Crystal data

C₁₉H₂₄O₄
M _r = 316.38
Triclinic,
a = 8.6163 (9) Å
b = 10.888 (1) Å
c = 11.261 (1) Å
α = 68.393 (2)°
β = 79.118 (2)°
γ = 67.998 (2)°
V = 909.09 (15) Å³
Z = 2
Mo Kα radiation
μ = 0.08 mm⁻¹
T = 293 K
0.48 × 0.46 × 0.42 mm

Data collection

Bruker SMART CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 2004 ▶) T _min = 0.760, T _max = 1.000
4986 measured reflections
3510 independent reflections
2759 reflections with I > 2σ(I)
R _int = 0.051

Refinement

R[F ² > 2σ(F ²)] = 0.055
wR(F ²) = 0.158
S = 1.04
3510 reflections
213 parameters
H-atom parameters constrained
Δρ_max = 0.22 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Data collection: SMART (Bruker, 2001 ▶); cell refinement: SAINT (Bruker, 2001 ▶); data reduction: SHELXTL (Sheldrick, 2008 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and DIAMOND (Brandenburg, 1998 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053681001367X/lx2139sup1.cif

e-66-o1103-sup1.cif^{(20.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053681001367X/lx2139Isup2.hkl

e-66-o1103-Isup2.hkl^{(172.1KB, 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
C2—H2⋯O1ⁱ	0.98	2.44	3.407 (2)	170

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors thank the EPSRC for financial support.

supplementary crystallographic information

Comment

Endocyclic enol lactones are important structural elements of biologically active natural products (Zhao et al., 1997) and useful synthetic intermediates for organic synthesis (Evans et al., 2005, Davies et al., 2004). The cyclization of alkynoic acids under acidic conditions (Krafft et al., 1981) , employing transition-metal complexes as catalysts (Zeni et al., 2004, Valerga et al., 2001),and the carbonylation coupling of alkynes and 1,3-dicarbonyl compounds are main synthetic pathways for the preparation of Enol lactones (Li et al., 2007)

In the title compound as shown in Fig. 1, the six-membered lactone ring adopts an envelope conformation with the tert-butoxycarbonyl, isopropyl and phenyl groups attached to it. The tert-butoxycarbonyl and isopropyl groups occupy axial positions, and the phenyl group occupies equatorial position. The crystal packing (Fig. 2) is stabilized by weak intermolecular C—H···O hydrogen bonds between the pyran H atom and the oxygen of the C═O unit in pyran ring, with a C2—H2···O1ⁱ (Table 1).

Experimental

The title compound was obtained as a by-product in the copper-catalyzed tandem conjugate addition–cyclization–hydrolysis–decarboxylation reactions of alkynes and 5-alkylidene-Meldrum's acids (Jiao et al., 2009) acids as follows: To a mixture of CuBr (20 mg, 0.1 mmol), 1-ethynylbenzene (102 mg, 1 mmol) in H₂O : t-BuOH = 10 : 1 (3 ml) was added and 2,2-dimethyl-5-(2-methylpropylidene)-1,3-dioxane-4,6-dione (99 mg, 0.5 mmol) at room temperature. The resulting mixture was refluxed for 10 h monitored by TLC. After evaporation, the residue was carefully purified by flash chromatography on silica gel. The title compound was obtained as a by-product (25% yield), which was crystallized from n-hexane-ethyl acetate.