The 7-(2-bromoethyl) derivatives, 2a and 2b, of 4-chloro-7H-pyrrolo [2,3-d]pyrimidine (1a) and 4-chloro-7H-pyrrolo[2,3-d]pyrimidin-2-amine (1b) were synthesized by nucleobase anion alkylation (NaH, DMF) and crystallized. X-Ray analyses of both compounds were performed, and they revealed significantly different positioning of the side chain relative to the heterocyclic ring, depending on the substituent (H or NH 2 ) at C(2).Introduction. -7-Deazapurines (¼ pyrrolo[2,3-d]pyrimidines 1 )) are of considerable importance, because a series of nucleoside antibiotics comprising tubercidin, toyocamycin, and sangivamycin contains the 7-deazaadenine moiety, while other naturally occurring nucleosides such as queuosine, cadeguomycin, and archaeosine contain a 7-deazaguanine ring [1] [2]. 7-Deazapurines of the xanthine type have been prepared as analogues of potent A1-and A2-adenosine receptor antagonists [3]. Functionalized derivatives of 7-deazapurines are of interest, because they can be easily coupled to polymers, dendrimers, lipids, or solid surfaces carrying amino functions, which lend them the functionality of a particular modified nucleobase [4 -6]. The coupling of the newly prepared compounds to redox-active dendrimers and their use as electrochromic materials will be published separately.