Azides, propargylic synthesis

This section covers cyclizations to the pyrrole nucleus catalyzed by other metals (Ti, Mn, Ru, Pd, Pt, Zn, In). Dembinski and co-workers used zinc(II) chloride as ligand-free catalyst for the microwave-assisted cyclization of homopropargyl azides 26 to afford substituted pyrroles 27 (Scheme 8) [62]. A similar methodology for the synthesis of 2,4,5-trisubstituted pyrroles was described by Driver et al. employing substituted 1-azidobuta-l,3-dienes in a cyclization reaction using catalytic amounts of zinc(ll) iodide [63]. A three-component zinc-catalyzed one-pot cyclization of aromatic and aliphatic propargylic acetates, silyl enol ethers, and primary amines to substituted pyrroles has been described by Zhan et al. The reaction sequence includes propargylation of the silyl enol ether, amination, 5-exo-(7ig-cyclization, and isomerization [64]. Hiroya and co-workers have shown... 

Intramolecular cycloaddition of an azide to an acetylenic bond offers a route to the synthesis of [l,2,3]triazolo[l,5-a][4,l]benzoxazepines (Scheme 16) <94H(38)291>. Considering the ready availability of the starting material (isatoic anhydrides and propargyl alcohols) this offers an attractive route to these compounds. 

The synthesis of cyclodextrin-like triazoles and macrocyclic carbohydrate/amino acid hybrids has been reported by Bodine et al. [66,67] and Billing et al. [68], respectively, through a common strategy based in the convergent cyclization of bifunctional azide/alkyne carbohydrate derivatives. Thus, Bodine et al. [66,67] prepared 2,3,6-tri-O-benzyl propargyl-a-D-mannopyranosyl... 

Figure 12.10 Synthesis of l,2-bis(2-azidoethoxy)ethane (VI), used as the bis(azide) core, from l,2-bis(2-chloroethoxy)ethane. (b) Synthesis of propargyl ether of l-hydroxybenzene-3,5-dimethanol (VII), used as a...

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