TETRAHEDRON LETTERS Pergamon Tetrahedron Letters 40 (1999) 8291-8293 Single electron transfer reductive cleavage of the aryl-nitrogen bond in phenyl-substituted dimethylanilines U. Azzena, F. Dessanti, G. Melloni * and L. Pisano Diparrimenlo di Chimica, UniversiG di Sassari, via Vienna 2, I-07100 Sassari, Italy Received 3 August 1999; revised 6 September 1999; accepted 14September 1999 Abstract By treatment with Li metal in THF at room temperature the three isomeric N,N-dimethylaminobiphenyls and NJ-dimethyl-2,6-diphenylanilineunderwent 100%regioselectivereductive cleavageof the aryl-N bond, affording biphenyl and me&-terphenyl, respectively, in various yields. 0 1999Publishedby Elsevier Science Ltd. All rights reserved. Keywords: reduction; electron transfer; bond cleavage; regioselectivity; deamination. The cleavage of strong covalent bonds by reductive single electron transfer (SET) is an object of present interest,’ focused on both its mechanistic aspects2 and synthetic usefulness,3 as well as on the discovery of hitherto unknown fragmentations. As an extension of our study of mechanisms2g*h,4 and synthetic applications’ of the SET reductive cleavage of C-O bonds in aryl alkyl ethers, in which we have shown that under appropriate conditions the scission of the aryl-0 bond in anisole and many substituted anisoles may compete favorably with that of the Me-O bond, we took into consideration the possibility of obtaining scission of C-N bonds of aromatic amines. This subject has received little attention, likely due to the low electron affinity of such substrates;only a few reports can be found in the literature.&’ We wish to report here that by simple treatment with Li metal in THF at room temperature the three isomeric NJ-dimethylaminobiphenyls l-3 and 2,6-diphenyl-N,N-dimethylaniline 4 undeyent exclusive Ar-N bond cleavage to afford bipheny15 and meta-terphenyl6, respectively (Scheme 1). The reductive cleavage was carried out as follows. Li metal (30% wt dispersion in mineral oil, 2 equiv.) was placed under Ar in a two-necked flask equipped with reflux condenser and magnetic stirrer, washed with THF (3x10 mL), and suspended in anhydrous THF (25 mL). To this well stirred suspension a solution of the appropriate substrate l-4 (2.5 mmol) in THF (5 mL) was added dropwise. The mixture was stirred at room temperature for 24 h and then quenched by slow dropwise addition of Hz0 (10 mL) (caution). Extraction with Et20 and standard workup afforded products 5 or 6, which were identified by GC-MS and purified by flash chromatography (hexane/EtOAc). * Corresponding author. Tel: +39079 229547; fax: +39079229559; e-mail:melloni@ssmain.uniss.it 0040-4039/99/$ - see front matter 0 1999 Published by Elsevier Science Ltd. All rights reserved PI/: s0040-4039(99)01758-x