Synthesis and structure investigations of N -arysulfinyl-1,4-benzoquinonemonoimines

Stable N -arylsulfinyl-1,4-benzoquinonemonoimines have been obtained by oxidation of N - arylthio-1,4-benzoquinonemonoimines with m -chloroperbenzoic acid. The N -arylthio-1,4-benzoquinonemonoimines can be oxidized to N -arylsulfonyl-1,4-benzoquinonemonoimines. Comparative structural studies of various quinoneimines by X-ray analysis have shown that in molecule of N -arylsulfinyl-1,4-benzoquinonemonoimine an interaction of the π -orbital of the S=O bond with the π -electron cloud of the benzene ring is observed, similar to that found in N - aroyl-1,4-benzoquinonemonoimines


Introduction
We have previously reported the first synthesis of stable N-arylsulfinyl-1,4benzoquinonemonoimines by reaction of 1,4-benzoquinonemonooximes with arylsulfinyl chlorides. 1The mechanism was postulated as occurring via the formation of N-arylsulfinyl-1,4benzoquinonemonoimines by conversion of 1,4-benzoquinonemonooximes to 1,4benzoquinonemonoimines accompanied by conversion of bivalent to a tetravalent sulfur .The major problem of this method was the formation of by-products, which were difficult to separate from the major product.
The only similarity is the interaction of the S=O (C=O) bond π-orbitals with the π-electronic cloud of benzene ring for 2i, 5, and 6 as mentioned above.The carbonyl of N-aroyl-1,4benzoquinonemonoimine is perpendicular to the plane of the quinone ring, 5 which promotes interaction of the π-orbital of C=O group with lone pair on nitrogen (n N ) (π C=O →n N ).Consequently the energy of E,Z-isomerization in the quinone imine 5 is low at 43,0 kJ/mol. 7In N-arylsulfinyl-1,4-benzoquinonemonoimine 2i the S=O group lays almost in the plane of quinone ring, enabling S=O group π*-orbital interaction with the lone pair on nitrogen (n N ).
The analysis of the shortened contacts shows, that the angle C=N-S for quinoneimines 2, 4, 5, 6, is close to 126 о , due to significant steric strain between the atom of oxygen (nitrogen) of group S=O (C=O, C=N) and carbon and hydrogen atoms of the quinone ring.For quinone imine 1 and quinoneoximes 7, 8 the steric strain of similar fragments is smaller, and a smaller value of the C=N-X angle is observed.
In spite of the significant differences of quinone imines and quinone oximes considered above, the length of C=N bond is practically constant within the limits of 1.29-1.30Å.That can Page 65 © ARKAT USA, Inc be construed as evidence for the similar mode of conjugation in quinone imines and quinone oximes (C=N-C=C-С=О) and an insignificant influence of constituents at nitrogen atom on it.Lengths of N-X and X-C Ar bonds in some cases are different from average values reported for similar bonds 10 (these values for comparison are given in brackets).The length of N-S bond of quinone imine 1i is 1.663 Å (1.656 Å), for quinone imine 2i -1.666 Å, and for quinoneimine 4 -1.660Å (1.642 Å).The length of N-C Ar bond for quinone imine 5 is 1.398 Å (1.355 Å), for quinone imine 6 -1.381 Å (1.355 Å).The length of N-O bond for quinone oxime 7 is 1.418 Å (1.416 Å), for quinone oxime 8 -1.419 Å (1.416 Å).The length of S-C Ar bond for quinoneimines 1i, 2i, and 4 is 1.761 Å (1.773 Å), 1.807 Å (1.790 Å), and 1.740 Å (1.788 Å), respectively.Thus, lengths of N-S bond are independent on sulfur state of oxidation for all three compounds 1i, 2i, 4.
It is necessary to note, that for quinoneimines 5 and 6 the N-C Ar bond is longer, than for similar compounds. 10The length of C-C Ar bond for quinoneimines 5 and 6 is 1.481 and 1.466 Å (1.500 Å), respectively.Longer N-C Ar bond and shorter C-C Ar bond additionally prove the πinteraction of C=O group with benzene ring [π С=О →π(C 6 H 6 )].To the best of our knowledge bond lengths of N-S IV and S IV -C Ar have been not reported.For this reason we were not able to perform similar structural comparison for quinone imine 2i.

Conclusions
A new synthetic route to N-arylsulfinyl-1,4-benzoquinonemonoimines is described.Based on the X-ray results and comparisons with literature data for the N-aroyl-1,4-benzoquinonemonoimines there is π-interaction between the S=O bond and the π-electronic cloud of the benzene ring of Narylsulfinyl-1,4-benzoquinonemonoimines.The angle at sulfur in N-arylsulfinyl-1,4benzoquinonemonoimines is typical of sulfoxides.

Experimental Section
General Procedures.All melting points are uncorrected. 1H-NMR spectra (300 MHz) were measured on a Varian VXR-300 spectrometer.Chemical shifts (δ) are given from TMS (0 ppm) as internal standard for 1 H-NMR; CDCl 3 was used as solvent.For thin-layer chromatography, Silufol UV-254 plates were used with -benzene-hexane (1:10) as eluent and development by UV light.
X-ray study of compound 1i.Analysis of monocrystal with linear sizes 0.22 x 0.43 x 0.49 mm was carried out at room temperature on automatic tetracircle diffractometer Enraf-Nonius CAD-4 (CuК α -radiation, λ 1.54178 Å, the relation of speeds of scanning 2Ө/ω 1.2, Ө max 70 о , a segment of sphere 0 ≤ h ≤ 14, 0 ≤ k ≤ 16, -15 ≤ l ≤ 15).Altogether 3982 reflections were collected from which 3656 were symmetry independent (R int 0.052).Crystals of compound 1i are monoclinic, a 12.171(8), b 13.626(8), c 12.941(8) Å, V 2003(2) Å 3 , M 372.5, Z 4, d calc 1.23 g/sm 3 , µ 15.6 sm -1 , F (000) 795.3, space group P2 1 /n (N 14).The structure is deciphered by a direct method and specified by a method of the least squares in fullmatri anisotropic approximation using the CRYSTALS program package. 11For specification the 1986 reflections with I >3σ(I) were used (235 adjustable parameters, number of reflections on parameter 7.2).All atoms of hydrogen were revealed from differed synthesis of electronic density and included in specification with the fixed position and thermal parameters.For specification the weight scheme of Chebushev 12 with four parameters was used: 0.65, -1.06, -0.09, and -0.64.Final values of factors of divergence R 0.059 and R W 0.057, GOF 1.130 were obtained.The residual electron density from differed Fourier series is 0.26 and -0.29 е/Å 3 .The calculation of absorption in a crystal was carried out by the method of azimuthal scanning. 13X-ray study of compound (2i).Analysis of a monocrystal with linear sizes 0.22 x 0.33 x 0.34 mm was carried out at room temperature on automatic tetracircle diffractometer Enraf-Nonius CAD-4 (CuК α -radiation, λ 1.54178 Å, the relation of speeds of scanning 2Ө/ω 1.2, Ө max 60 о , and a segment of sphere 0 ≤ h ≤ 18, 0 ≤ k ≤ 13, -11 ≤ l ≤ 11).Altogether 3356 reflections were collected from which 3063 were symmetry independent (R int 0.033).Crystals of compound 2i are monoclinic, a 16.319( 8), b 12.60(6), c 10.460(9) Å, V 2071(2) Å 3 , M 388.5, Z 4, d calc 1.25 g/sm 3 , µ 16.1 sm -1 , F (000) 824.0, space group P2 1 /c (N 14).The structure is deciphered by a direct method and specified by a method of the least squares in fullmatri anisotropic approximation using the CRYSTALS program package. 11For specification the 2280 reflections with I>3σ(I) were used (244 adjustable parameters, number of reflections on parameter 9.3).About 80% atoms of hydrogen were revealed from differed synthesis of electronic density; positions of other hydrogen atoms were calculated geometrically.All hydrogen atoms were included in specification with the fixed position and thermal parameters.For specification the weight scheme of Chebushev 12 with five parameters was used: 1.76, -0.77, 0.64, -0.74, and -0.24.Final values of factors of divergence R 0.062 and R W 0.065, GOF 1.068 were obtained.The residual electron density from differed Fourier series is 0.43 and -0.24 е/Å 3 .The calculation of absorption in a crystal was carried out by a method of azimuthal scanning. 13nitial quinoneimines 1a,b,d,f,g were obtained by a literature method 14 and crystallized from ethanol.Quinoneimines 1j,k were obtained as described earlier 16 .The spectral characteristics of quinoneimines 1c,e,h 15 and 1i 1 are identical to those reported earlier.General procedure for oxidation of N-arylthio-1,4-benzoquinonemonoimines 1a-k to Narylsulfinyl-1,4-benzoquinonemonoimines 2a-k MCPBA (460 mg, 2 mmol) (commercial, the content of the basic substance 70-75%) was added to a solution of corresponding N-arylthio-1,4-benzoquinonemonoimine 1a-k (2 mmol) in 40 mL methylene chloride at room temperature with stirring.Stirring was continued within two hours.Completion of reaction was monitored by the TLC method.The solution was filtered, and the filtrate was evaporated under reduced pressure.The obtained mixture was washed with 10% solution of sodium bicarbonate, the solvent removed, the residue was dried and crystallized from petroleum-ether (boiling-point 40-70 о С).Compounds 2j,k were crystallized from octane.The quinoneimines 2j,k are identical to those described earlier.General procedure for oxidation of N-arylthio-1,4-benzoquinonemonoimines 1c,h to Narylsulfonyl-1,4-benzoquinonemonoimines 3c,h MCPBA (2.2 mmol) (commercial, the content of the basic substance 70-75%) was added to a solution of quinonemonoimine 1c,h (2 mmol) in 20 mL methylene chloride at room temperature with stirring.Stirring was continued for one hour.The completion of the reaction was controlled by the TLC method.After evaporation of the methylene chloride the residue was washed with water and crystallized from glacial acetic acid.The obtained compounds 3c (yield 55%) and 3h (yield 60%) were identical with those previously described. 17