Syntheses and crystal structures of two dinaphtho[2,1-d:1′,2′-f][1,3]dithiepine atropisomers

The molecular and crystal structures of 1-(dinaphtho[2,1-d:1′,2′-f][1,3]dithiepin-4-yl)-2,2-dimethylpropan-1-ol and 2-(dinaphtho[2,1-d:1′,2′-f][1,3]dithiepin-4-yl)-3,3-dimethylbutan-2-ol, from asymmetric syntheses are reported.


Structural commentary
The structural core of compounds 1 and 2 is a 1,1 0 -linked binaphthalene system. This is functionalized at the 2,2 0 positions with a disulfaneylmethane unit, generating a sevenmembered ring with pseudo-C 2 symmetry locking the binaphthalene into R and S atropisomers. The individual naphthalene ring systems in 1 are predictably flat, with r.m.s. deviations from the ten-atom mean plane of 0.019 and 0.022 Å for C101-C110 and C201-C210 respectively. The C102-C101-C201-C202 torsion angle is À62.5 (3) and the dihedral angle between naphthalene ring mean planes is 65.91 (4) . Capping the stereogenic auxiliary is a chiral (at atom C2) neopentyl alcohol group (Fig. 1), giving aS,R and aR,S pairs. The synthesis of compound 2 (Fig. 2) places a methyl group on the chiral C2 atom in place of the hydrogen atom of 1. This juxtaposition generates a racemate pair with similar conformation and metrics to 1 (Fig. 3): r.m.s. deviations from the naphthalene mean planes are 0.05 and 0.04 Å and the C102-C101-C201-C202 torsion angle is À63.95 (19) , however the dihedral angle between naphthalene rings is larger at 72.35 (3) . The alcohol group is positioned such to form an intramolecular hydrogen bond to one of the bridge sulfur atoms (O2-H2OÁ Á ÁS1 = 2.52 Å ).  The molecular structure of 2 with displacement ellipsoids drawn at the 50% probability level.

Figure 1
The molecular structure of 1 with displacement ellipsoids drawn at the 50% probability level.

Figure 3
The molecular structures of 1 (left) and 2 (right) aligned with the C101-C201 bond on the z-axis. The intramolecular C-HÁ Á ÁS bond of 2 is shown as a red dotted line.

Figure 6
Twofold screw of 2 in the b-axis direction formed by C-HÁ Á Á interactions (blue dotted lines); Cg2 is the C105-C110 ring centroid.

Figure 7
Glide reflection of 2 in the bc plane formed by C-HÁ Á Á interactions (blue dotted lines); Cg4 is the C205-C210 ring centroid.

Synthesis and crystallization
Compounds 1 and 2 were synthesized in three steps (Fig. 8) from dithiepin 3 prepared from a Lewis-acid-catalysed condensation of binaphthothiol with dimethoxymethane (Delogu et al., 1991). Diastereoisomer mix (4) (5): to a stirred solution of alcohol 4 in CH 2 Cl 2 was added CaCO 3 and powdered 4 Å molecular sieves. PCC (3.3 equiv.) was added and the reaction mix stirred (30 min, Ar, RT). The solvent was concentrated in vacuo and filtered through SiO 2 to give the ketone as a white solid, m.p.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were refined using a riding model with d(C-H) = 0.95 Å , U iso = 1.2U eq (C) for aromatic H, 1.00 Å , U iso = 1.2U eq (C) for CH, 0.98 Å , U iso = 1.5U eq (C) for methyl H atoms and d(O-H) = 0.84 Å , U iso = 1.5U eq (O) for OH. For both structures, data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998). Data reduction: SAINT (Bruker, 19980) for (1); SAINT (Bruker, 1998) for (2). For both structures, program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2019/2 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2019/2 (Sheldrick, 2015b) and publCIF (Westrip 2010).  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.