TETRAHEDRON LETTERS Tetrahedron Letters 40 (1999) 767-770 Pergamon A Facile Radical Induced Selective Removal of N-Propargyl Protecting Groups Using Low Valent Titanium Reagents Shyam Rele, Sanjay Talukdar and Asoke Banerji*l Bio-Organic Division, Bhabha Atomic Research Centre, Trombay, Mumbai - 400 08J, India. Received 4 September 1998; accepted 10 November 1998 Abstract: Low valent titanium mediated cleavage of N-propargyl bonds offers a facile, mild, and high yielding method for the deprotection of amines under neutral conditions. The methodology could be used for the chemoselective removal of propargyl groups ~orn amines in preference to the allyl/henzyl counterparts and can be performed chemoselectively in the presence of methoxy, methylenedioxy, and chloro functionalities. © 1999 Elsevier ScienceLtd. All rights reserved. Keywords: N-Propargylamines; Selectivedeprotection; Low valent titanium Desiring efficient protecting groups is often a decisive factor in many demanding synthetic projects [1 ]. In particular, amino protection is of paramount importance for the synthesis of many compounds, including peptides [2,3]. A wide range of reagents has been developed for this purpose. Towards this end, a conceptually new approach to radical induced selective deprotection of N-benzyl/allyl amines was reported by us [4-6]. However, the yields were moderate and the reaction required prolonged reflux (-22 h). The yield of the reaction could be substantially improved by using the activated low valent titanium (LVT) reagent recently described by us [7], but methoxy and chloro groups were cleaved under the reaction conditions. This incompatibility of functionalities prompted us to develop better protecting groups which could be liberated under milder conditions with good yields. The presence of two orthogonal n- bonds in the propargyl group makes it attractive as an efficient protective group for alcohols/phenols [8,9]. Based on these considerations, we anticipated that N-propargyl amines should undergo facile cleavage. Although the involvement of organometallic rl3-allylic complexes in a number of synthetic endeavors is well documented [10,11], the potential of propargylie organometallic derivatives has been less explored. In addition to our work [9], few methods for the cleavage of propargyl ethers have been reported [ 12,13,14]. Herein we wish IFax : 91-22-5505151; E-mail : abanerji@magnum.barc.ernet.in 0040-4039/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(98)02407-1