Science of Synthesis

Marsden, S. P., Science of Synthesis, (2005) 26, 1084.

The elimination of siloxides from β-lithioalkoxysilanes (the Peterson reaction) is a facile process for alkene synthesis. With regard to enone synthesis, such species would be created by the aldol condensation of lithium enolates of silylated ketones with carbonyl compounds. Thus, deprotonation of 1-(trimethylsilyl)heptan-2-one (‌215‌) under optimized conditions using 1-(trimethylsilyl)hexyllithium (‌216‌) as a base gives a 98:2 mixture of regioisomeric enolates ‌217‌ and ‌218‌, which upon condensation with aldehydes gives good yields of E-enones such as ‌219‌ (‌Scheme 40‌).[‌184‌] Despite the well-documented acidifying effect of silicon substituents, the use of lithium amide bases gives poorer mixtures of enolate isomers, and other workers have reported preferential formation of the undesired isomer, apparently through a steric blocking effect of the silicon substituent.[‌185‌] The reaction can be used to generate efficiently sensitive cyclopropyl vinyl ketones such as ‌221‌ from ‌220‌.[‌186‌] Silyl-substituted silyl enol ethers also undergo Lewis acid mediated aldol condensation/Peterson alkenation to yield the E-enones (e.g., conversion of ‌222‌ into ‌219‌).[‌184‌]

‌Meeeee 88‌ Meeeeeee Meeeeeeeee eeee α-Meeee Meeeeee[‌888‌,‌888‌]

Meeeeeeeeeee Meeeeeeee

(M)-Meeeeee-8-ee-8-eee (‌888‌); Meeeeee Meeeeeeee:[‌888‌]

Me e eeee ee 8-eeeeeeeeeeeeeeeeeeeeeeeeee [‌888‌; 8.88 eeee, eeeeeeee eeee MeMe eee eee­eeee­ee(eeeee)eeeeee] ee MMM (88 eM) ee −88°M eee eeeee e eeee ee 8-(eeeeeeeeeeeeee)eeeeee-8-eee (‌888‌; 8.88 eeee) ee MMM (8 eM). Meeee eeeeeeee eee eeeeeee ee −88°M eee 8 e, e eeee ee eeeeeee (8.88 eeee) ee MMM (8 eM) eee eeeee. Mee eeeeeee eee eeeeeee eee 88 eee ee −88°M eee eeeeeeee eeee eee. ee MM8Me (88 eM). Meeee eeeeeeeeee eeee MeMMe eee eeeeeeee eeeeeee eeeeee eeee eeeeee eeee eeeee eee eeeee (MeMM8). Meeeeeeeeee ee eee eeeeeee eee eeeeeeeeeeee ee eee eeeeeeee eee ee eeeeee eeeeeeeeeeeeee (eeeeee/MeMMe 88:8) eeee eeeee ‌888‌; eeeee: 88%.

References