2 (1)

274

1/4 Generation of C ^rza ~c~e:a 'z Reagents and Intermediates

a-Cumylpotassium (1 -methyl-l-phenylethylpotassiumf⁴⁴⁰*

CH(CH₃)₂

KCH₂Si(CH,)₃

CH,I

ę(CH₃)₃

Isopropylbenzene (cumerie; 0.50 mL, 0.43 g, 3.6 mmol) is added to a precooled solution of trimethylsilylmethylpotassium (see pp. 158 and 159, 3.6 mmol) in tetra-hydrofuran (5.0 mL). After 24 h at — 50 °C, the reaction is quenched with methyl iodide (0.30 mL, 0.68 g, 4.8 mmol). fe/t-Butylbenzene (74%) is identified by gas chromatograph as the sole product, no tracę of cymols (isopropyltoluenes) being present. When the metalation time is reduced to 2 h without increasing simultane-ously the concentration, the yield of re/t-butylbenzene drops to <10%.

4-( Dimethy lamino )benzylpotassium^^45] ^

CHy K

ch₂-ch₃

(H₃C0)₂S0₂

KOC(CH,)₃

N(CH₃)₂    N(CH₃)₂    N(CH₃)₂

At —75°C, butyllithium (15 mmol) in hexanes (10 mL) and potassium ten-butoxide (1.7 g, 15 mmol) are added to a solution of /V,N,p-trimethylaniline (NM-dimethyl-p-toluidine; 2.2 mL, 2.0 g, 15 mmol) in tetrahydrofuran (15 mL). The mixture is vigorously stirred until it becomes homogeneous, then kept 48 h at —75°C using a cryogenic unit. After the addition of dimethyl sulfate (1.4 mL. 1.9 g, 15 mmol), it is allowed to reach 25 °C. Gas chromatographic analysis by means of an internat reference substance (‘standard’) reveals the presence of 65% of jV,jV-dimethyl-/?-ethylaniline besides some unconsumed starting materiał. The main product is isolated by distillation (b.p. 96-97 °C/10 mmHg).

(E )-3,3-Dimethyl-1 -butenylsodium^¹⁴⁸⁹*

NaC$H||

(l.)CH2=0

NaO

ONa

Na

(2.)H

©

OH

3,3-Dimethyl-l-butene (3.0 mL, 2.0 g, 23 mmol) is added to the suspension of pentylsodium (20 mmol) and disodium pinacolate (20 mmol) in pentane (50 mL . After 50 h of rigorous stirring, the sealed Schlenk tubę is opened and the mixture is treated with a 0.8 M solution of formaldehyde^²⁰⁴⁴^ (10 mmol) in tetrahydrofuran (25 mL). After neutralization, 4,4-dimethyl-2-penten-l-ol having a (ZIE) ratio of 0.2:99.8 is isolated [b.p. 76-77 °C/20 mmHg; yield: 88%].