2254 J. zyxwvutsr Org. Chem. 1995,60, zyxwv 2254-2256 Hexamethyldisilathiane: Its Use in the Conversion of Aromatic and Heteroaromatic Azides to Amines Antonella Capperucci,? Alessandro Degl’Innocenti,*J Maria Funicello,g Giacomo Mauriello,$ Patrizia Scafato,$and Piero Spagnolo*J Centro CNR Composti Eterociclici, via G. Capponi, zyxwvut 9, 50121 Firenze, Italy, Dipartimento di Chimica, Universita della Basilicata, via zyxwvutsrqpo N. Sauro 85, 85100 Potenza, Italy, and Dipartimento di Chimica Organica “A. Mangini”, viale Risorgimento 4, 401 00 Bologna, Italy Received October 17, 1994 Introduction Several recent reports in the literature have demon- strated that hexamethyldisilathiane (HMDST) may be efficiently employed in the formation of thiocarbonyl compounds, including inter alia thioaldehydes, thioke- tones, thioamides and thio1actams.l Very recently, this thionating agent has been utilized in our laboratory to effect the conversion of aromatic and heteroaromatic o-azidoaldehydes to o-azidothioaldehydes, a new class of reactive thioaldehydes. Azidothioaldehydes were pro- duced by reacting the corresponding oxo compounds with HMDST in acetonitrile at room temperature and in the presence of hydrochloric acid or Lewis acids such as CoClz.6HzO and TMSOTf. According to the reaction conditions transient azidothioaldehydes underwent in- tramolecular cyclization to fused isothiazoles2 and/or intermolecular Diels-Alder reaction with 1,3-dienes to give thioaldehyde-diene cycloadd~cts.~ Now we wish to report that HMDST can also act as an efficient agent in the transformation of aromatic and heteroaromatic azides to amines. Results and Discussion Brief reaction of the zyxwvuts azidohetarenecarbaldehydes la-i (all previously known, except IC and d) with a 2-fold excess of HMDST in methanol, at room temperature, led to isolation of the corresponding aminoaldehydes 2a-i in good to fairly good yields (Table 1, entries 1-9). 2-Amino-3-formyl- (2h) and 3-amino-2-formylbenzo[bl- thiophene (2g) were previously obtained (but in moderate yields) by reduction of the nitro derivatives with iron powder and ammonium ~hloride.~ 3-Amino-2-formyl- thiophene (2b),5 3-amino-2-formylfuran (2a),5 and 2-amino- 3-formylbenzo[blfuran (2n6 were previously prepared by related reduction of the appropriate azide lb,a,f with T e n t r o CNR Composti Eterociclici. Wniversiti della Basilicata. “ipartimento di Chimica Organica “A. Mangini”. (l)(a) Smith, D. C.; Lee, S. W.; Fuchs, P. L. J. Org. Chem. 1994, 59,348 and references cited therein. (b) Degl’Innocenti,A.; Capperucci, A.; Mordini, A.; Reginato, G.; Ricci, A.; Cerreta, F. Tetrahedron Lett. 1993,34,873. (c) Capperucci, A.; Degl’Innocenti, A.; Ricci, A,; Mordini, A.; Reginato, G. J. Org. Chem. 1991, 56, 7323. (2) Degl’Innocenti, A,; Funicello, M.; Scafato, P.; Spagnolo, P. Chem. Lett. 1994, 1873. (3) Capperucci, A.; Degl’Innocenti, A,; Scafato, P.; Spagnolo, P. Chem. Lett. 1995, 147. (4)Chippendale, K. E.; Iddon, B.; Suschitzky, H. J. Chem. Soc., Perkin Trans. 1 1973, 129. (5) Gronowitz, S.; Westerlund, C.; Hornfeldt, A.-B. Acta Chem. Scand. Ser. B 1975,29, 224. (6) Becher, J.; Pluta, K.; Krake, N.; Brondum, K.; Christensen, N. J.; Vinader, M. V. Synthesis 1988, 530. hydrogen sulfide gas in the presence of base. On the other hand, the compounds 2c-e and 2i represent new examples of somewhat rare aminohetarenecarbaldehydes which are chemically stable due to delocalization of the amino-nitrogen lone pair.6 It is worth noting that hitherto known o-aminoaldehydes derived from five- membered heteroaryl systems are normally prepared by hydrogen sulfide reduction5s6of o-azidoaldehydes, which in turn can be obtained from o-halocarbaldehydes through nucleophilic aromatic substitution reaction with sodium azide in DMS0.2,5,6 The scope of this nucleophilic sub- stitution reaction is, however, not general since it may especially fail in the preparation of the a-azides owing to their tendency to suffer decomposition under (very) mild thermal conditions to give ring cleavage product^.^^^ Very recently we uncovered that 2-formyl-3-nitro- and 3-formyl-2-nitrobenzo[blthiophene readily react with so- dium azide in HMPA or DMSO, respectively, to give the azides lg,h in very satisfactory yielde2 In the present work a similar procedure proved to be effective to produce the previously unknown 2-azido- thiophenes IC and d. These unstable azides lc,d could in fact be obtained in zyxw 40 and 60% isolated yield through brief reaction of the corresponding nitro derivatives with sodium azide in HMPA at 0 “C. Prolonged reaction times and/or higher reaction temperatures resulted in essential decomposition of the produced azides. Previous attempts to prepare the azidothiophene IC, either through reaction of 2-bromo-3-formylthiophene with NaN35 or through azido transfer reaction of tosyl azide with 2-lithiated 3-formylthiophene ethylene acetalY8 proved to be totally unsuccessful. Similar to its heterocyclic analogs la-i, o-azidoben- zaldehyde zyxwv ( lk)9-12 was converted, under comparable conditions, into o-aminobenzaldehyde (2k) in good yield (Table 1, entry 11). This unprecedented reduction of o-azidobenzaldehyde (lk) is of interest especially since we succeeded in obtaining this azide, in virtually quan- titative yield, by direct reaction of o-nitrobenzaldehyde with sodium azide in HMPA. Consequently, we concomi- tantly disclosed a new clean method for the formation of o-aminobenzaldehyde from the nitro derivative. It is known that the reductions of o-nitrobenzaldehydes to aminoaldehydes are complicated by competing inter- and intramolecular condensation reactions of the intermedi- ate hydroxylamines, which often requires a critical choice of reducing agent.13 3-Azido-2-nitrobenzo[blthiophene (lj) newly prepared by nucleophilic substitution of 3-bromo-2-nitrobenzo[bl- thiophene by azide ion, as well as the nitro- and cy- anophenyl azides 11-0 were also found to undergo smooth reaction with HMDST to give the amines 2j,l-o in fairly high yields (Table 1, entries 12-15). Addition- ally, parent 2-azidobenzo[blthiophene lp was similarly converted into the amine 2p (Table 1, entry 16)) but (7) Funicello, M.; Spagnolo, P.; Zanirato, P. Acta Chem. Scand. 1993, 47, 231. (8) Spagnolo, P.; Zanirato, P. J. Org. Chem. 1978, 43, 3539. (9)o-Azidobenzaldehyde has been prepared by diazotization of o-aminobenzaldehyde oxime,1° by hydrolysis of o-azidobenzaldehyde azine,” or more recently, by oxidation of o-azidobenzyl alcohol with pyridinium chlorochromate.12 (10) Schwan, T. J.; Davis, C. S. J. Pharm. Sci. 1969, 57, 877. (ll)Anselme, J.-P.; Sakai, K. J. Org. Chem. 1972, 37, 2351. (12)Ardakani, M. A,; Smalley, R. K.; Smith, R. H. J. Chem. Soc., (13) Caluwe, P.; Tetrahedron 1980, 36, 2359. Perkin Trans. 1 1983, 2501. 0022-3263/95/1960-2254$09.00/0 63 1995 American Chemical Society