Labile compounds, preparation under protective conditions

PREPARATION OF LABILE COMPOUNDS UNDER PROTECTIVE CONDITIONS. CHROMIUM (II) SALTS... 

Labile compounds, preparation of, under protective conditions, 6 144... 

The use of indole salts is frequently required to achieve selective attack at the 3-position in the acylation reaction. However, this approach is not applicable to indoles bearing functional groups labile under basic conditions, and consequently, Grignard reagents or alkylzinc compounds cannot be used for the preparation of the indole salts as shown in Scheme 2.2. A second approach involves the use of N-protected indoles and requires protection-deprotection steps. 

Routes to 8-fluoropurines had been limited until recently. However, an efficient one-step synthesis was reported in 1996 that has made available these compounds for a variety of studies. Thus, reaction of a series of protected oxopurines and protected adenosine with 1% F2 in He gave the corresponding 8-fluoro derivatives in 25-30% yields (Fig. 3.60). 2, 3, 5 -Tri-0-acetyl-8-fluoroadenosine so prepared was found to undergo defluorination under normal conditions of deprotection. A thermal labile hydrolase was subsequently used to effect this deprotection to produce, for the first time, free 8-fluoroadenosine. More detailed studies on the mechanism of defluorination of 8-fluoropurines indicated that acidic conditions are incompatible with 8-fluoroguanine and 8-fluoroadenosine while basic conditions are also incompatible... 

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