6-[(tert-Butyldimethylsilyl)oxy]-3-ethenyl-7-methoxy-4-[(trimethylsilyl)ethynyl]naphtho[2,3-c]furan-1(3H)-one

In the molecule of the title compound, the tricyclic core, consisting of a naphthalene entity fused together with a furan ring, deviates slightly from planarity.

The tricyclic core in the title compound, C 26 H 34 O 4 Si 2 , shows disorder of the furan ring and deviates slightly from planarity, with the largest displacement from the least-squares plane [0.166 (2) Å ] for the major disordered part of the methine C atom. To this C atom the likewise disordered vinyl group is attached, lying nearly perpendicular to the tricyclic core. In the crystal, mutual C-HÁ Á Á interactions between the methine group of the furan ring and the central ring of the tricyclic core of an adjacent molecule lead to inversion-related dimers.

Structure description
Notoincisol B is a naturally occurring polyenyne-hybrid compound, which was found to act as a promising partial agonist at the nuclear receptor PPAR (Liu et al., 2014). Attempting to make this novel scaffold synthetically accessible, a biomimetic pathway towards notoincisol B has been investigated (Kremsmayr, 2017). Within the proposed synthetic route, the lactone analogue of the characteristic tricyclic notoincisol B core structure was obtained via an intramolecular dehydro-inverse-electron-demand Diels-Alder-type cyclization reaction between a styrene and an alkyne moiety. Cyclization of a simplified notoincisol B model precursor substrate afforded the title compound, along with equal quantities of a regioisomer and proved the synthetic feasibility of this key-step reaction (Fig. 1).
The molecular structure of the title compound is displayed in Fig. 2. A naphthalene entity to which a furan ring is fused makes up the tricyclic core of the molecule, consisting of twelve C atoms (C1-C12) and one O atom (O1). Parts of the furan ring (O1, C12) and the attached vinyl group (C13, C14) are disordered over two sets of sites. The tricyclic data reports core is non-planar, with an r.m.s. deviation of fitted atoms from the least-squares plane of 0.0778 Å . The highest deviation is 0.166 (2) Å for C12 (considering the major disordered part), which is also the atom to which the vinyl group (-C13 C14) is attached. The latter is nearly perpendicular to the tricyclic core, with a dihedral angle of 85.2 (2) between the two moieties. The angle between the C10 atom of the tricyclic core and the attached ethynyl group (-C15 C16-) is slightly bent [175.98 (16) ], just like the angle between the ethynyl group and the Si1 atom of the trimethylsilyl (TMS) group [178.46 (16) ]. Fig. 3 shows the packing of individual molecules in the crystal. The bulky tert-(butyldimethylsilyl)oxy (TBDMSO) and trimethylsilyl (TMS) groups preventstacking, and the only remarkable intermolecular interaction between two adjacent molecules are mutual weak C-HÁ Á Á contacts. This involves the methine group (C12-H12) of the furan ring and the centroid of the central ring (C2,-C11; Cg1) of the tricyclic core [C12-H12Á Á ÁCg1(1 À x, 1 À y, 1 À z); H12Á Á ÁCg1 = 2.63 Å , C12Á Á ÁCg1 = 3.622 (3) Å , C12-H12Á Á ÁCg1 = 171 ]. In this way, inversion-related dimers are formed (Fig. 3).

Synthesis and crystallization
The synthesis followed a reported procedure (Kocsis & Brummond, 2014). A 20 ml microwave vial, equipped with a stirring bar, was charged with 7-(trimethylsilyl)hepta-1-en-4,6diyn-3-yl (E)-3-{4-[(tert-butyldimethylsilyl)oxy]-3-methoxy-phenyl}acrylate (0.400 g, 0.85 mmol, 1.00 equiv.), m-xylene (12.6 ml) and PhNO 2 (1.4 ml 10% (v/v%) in m-xylene, final molarity c = 0.06 M). The vial was sealed and heated via microwave irradiation to 453 K for 15 min, resulting in a colour change from a light-green to a dark-brown solution (reaction progress was checked with TLC, Lp: EtOAc = 10:1). Upon completion, the crude mixture was transferred into a flask and solvents were evaporated under high vacuum at 333-343 K. The two resulting regioisomers were separated via flash chromatography (180 g SiO 2 , flow rate 50 ml min À1 , using gradient Lp to Lp: EtOAc = 10:1 in 30 min, then 10:1 isocratically 10 min), affording 0.160 g (40%) of the title compound as a beige solid and 0.151 g (38%) of its regioisomer as a yellow oil. The title compound was recrystallized from ligroin, affording colourless material.  View of the crystal packing along [100]. Mutual C-HÁ Á Á interactions (green lines) lead to the formation of inversion-related dimers, as emphasized in the middle of the unit cell. For clarity, only the disordered part with major contribution is shown.

Figure 1
Reaction scheme to afford the title compound along with its regioisomer.

Figure 2
The molecular structure of the title compound, showing anisotropic displacement ellipsoids at the 50% probability level. The disordered part with a minor contribution is shown with open bonds.

data-1
IUCrData ( Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.