The preparative scale synthesis of dimesityldioxirane (5) via oxidation of dimesitylcarbene (6) is described. The dioxirane was obtained as colorless crystalline material, completely stable at −20 °C and characterized by spectroscopic methods, X-ray crystallography, and DFT calculations (B3LYP/6-31G(d)). The molecule shows approximately local C 2 symmetry with the mesityl rings twisted by ca. 60°. The experimental structural parameters, e.g., the O−O distance of 1.503 Å, are in good agreement with the theoretical values. The relief of steric strain caused by the mesityl groups is discussed in terms of the geometric distortion of the three-membered ring and the mesityl groups. Conformational features of 5 in solution are nicely reflected by measured and calculated (SOS-DFPT) NMR chemical shifts.

A modified version of the Bischler indole synthesis has been developed in which the key step is the N-H insertion reaction of rhodium carbene intermediates derived from α-diazo-β-ketoesters with anilines. Thus N-methylanilines 1 react with diazoketoesters 2 in the presence of dirhodium() acetate to give (N-arylamino)ketones 3, cyclisation of which using boron trifluoride-ethyl acetate or acidic ion exchange resin gives the indoles 4. In order to extend this method to the synthesis of N-unsubstituted indoles, a new protecting group strategy for indoles was developed. In this, anilines are reacted with α,β-unsaturated-esters or -sulfones to give the conjugate addition products 6 and 9, cyclisation of which gives indoles 8 and 11. The N-(2-ethoxycarbonylethyl)-and -(2-sulfonylethyl)-protecting groups are readily removed from indoles 8 and 11 by treatment with base.

No abstract

No abstract

A . -D Schluter. A h . M c i t w 1991. 3. 282 291.[2] S. Kivelsoii, 0 . L Chapman. P h n . Kcv. B 1983. 18, 72.36 7243. [3] L. Yu. M. Chen. I.. R. Dalton. C'/irm. M a r c r . 1990, 2. 649-659. [4] J. . I Bredas. R. Silbcy. Coiiliqrirrd Pol~nii~rs, Tlic ,Vow/ S(,ioicr cmri l i~h n o l o g i~ of Hi,ahli Condiir /in,? and .Vonlinrar Opric cdls A < r i v e lWor~~riul,s. Kluwcr. Dordrccht. 1991 151 M. Schwoercr. P / I~ Bl. 1994. 5 0 . 52-58. [h] First example A -D. Schluter. M. Ldller. V. Eiikclmanii, ,Vrirnrc, 1994. 36K. 831 -834. [7] H. Schirnier. A.-D. Schluter. V. Eiikelinann, C/lein. Brr. 1993. 126. 343-2546, [8] M. Liiffler. A.-D. Schliiter. SI-ii/c,ri 1994. 75-78. [9] See Tor example M. Ballauff. A n p m . Clwni. 1989. 101. 261 -276. Anjicu . Cllmi.[lo] Single cr\,stals of' 7 were wown from toluene. 6565 uniuue reflcctions were 1/11, E d /+,a/. 1989, 28-253-267. L -collected on a n Enraf-Nonius Turbo-CAD4 difTractonieter with Ni-filtered Cu,, radiation from ii rotating-anode generator. (/. = 1.542, " 1 ' 2 0 scan mode. Y,,,,, = I20 . nominal resolution ;.;2 sin Om, , = 0.89 A. Y scan absorption corredion. T = 260 K ) . The data &ere corrected for radiation damagc (12% reduction in intensity of three relerence reflections) Space group triclinic. P I . Z = 2 with two toluene per formula unit i n the asymmetric unit. N = 12.390(4). h = 16.164(6). = lX.96(2) A, 2 = 87 67(5). p = 83.30(5). ;' = 68.66(3) , V = 3514(4) A'. The structure was determined by direct methods using program SIR92 and refined with SHELX76 and SHELX93 on the basis of 3643 rellections with \(,I t 3o-(lfJ). H atoms bonded to the aroin:itic <-atoms were placed in their calculated positions. TWJ atoms in one of the aliphatic cliains.C45 and C49 are tnofold disordered with 0.5 occupancy. The cocrystallired toluene inolecules are fully ordered. The relatively high crystallographic R mciated with radiation damagc ofthe crystal. with only 5 5 % of the data above .3z (l~,l). and with the atom disorder. The extended aromatic system is x~irtn~111~ planar: with iio atom deviatiiig more than 0.105 A from the weighted least-squues plane [I I ] Further details of the crystal btructure investigation may be obtained from the ~achinforiiiationczentruin Karlsruhe. D-76344 Eggenstein-Leopoldshafen on quoting the depository number CSD-5X461.