Lithium, organo- compounds synthesis using

In many syntheses activation is not effected by sonochemical preparation of the metal alone but rather by sonication of a mixture of the metal and an organic reagent(s). The first example was published many years ago by Renaud, who reported the beneficial role of sonication in the preparation of organo-lithium, magnesium, and mercury compounds [86]. For many years, these important findings were not followed up but nowadays this approach is very common in sonochemistry. In another early example an ultrasonic probe (25 kHz) was used to accelerate the preparation of radical anions [87]. Unusually for this synthesis of benzoquinoline sodium species (5) the metal was used in the form of a cube attached to the horn and preparation times in diethyl ether were reduced from 48 h (reflux using sodium wire) to 45 min using ultrasound. 

Many syntheses of useful compounds utilize the nucleophilic addition of a Grignard or organo-lithium reagent to form carbon-carbon bonds. For example, a key step in the synthesis of ethy-nylestradiol (Section 11.4), an oral contraceptive component, is the addition of lithium acetylide to a ketone, as shown in Figure 20.5. 

Ideally it should be possible to add organo-Li and Grignard reagents to prochiral aldehydes and ketones with a chiral catalyst to give alcohols in good enantiomeric excess. This is difficult since the uncatalysed rate of addition is so high. It is possible to add the less reactive lithium acetylides such as 207 to ketones in the presence of stoichiometric lithium derivatives of amino alcohols such as 209, analogues of ephedrine. The product 208 is used in the asymmetric synthesis of the Merck anti-HIV compound Efavirenz.47... 

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