Bu4N+-Controlled Addition and Olefination with Ethyl 2-(Trimethylsilyl)acetate via Silicon Activation

Abstract

Catalytic Bu4NOAc as silicon activator of ethyl 2-(trimethylsilyl)acetate, in THF, was utilized for the synthesis of β-hydroxy esters, whereas employing catalytic Bu4NOTMS gave α,β-unsaturated esters. The established reaction conditions were applicable to a diverse range of aromatic, heteroaromatic, aliphatic aldehydes and ketones. Reactions were achieved at room temperature without taking any of the specialized precautions that are in place for other organometallics. A stepwise olefination pathway via silylated β-hydroxy esters with subsequent elimination to form the α,β-unsaturated ester has been demonstrated. The key to selective product formation lies in use of the weaker acetate activator which suppresses subsequent elimination whereas stronger TMSO– activator (and base) facilitates both addition and elimination steps. The use of tetrabutyl ammonium salts for both acetate and trimethylsilyloxide activators provide enhanced silicon activation when compared to their inorganic cation counterparts.

A green Heck reaction protocol towards trisubstituted alkenes, versatile pharmaceutical intermediates

“…R f : 0.3 (hexane/AcOEt 95:5 v/v). 1 H-NMR consistent with literature ( Tyagi and Fasan, 2016 ; Das et al, 2017 ) (see Supplementary Material ).…”

Phosphine-Mediated Sequential [2+4]/[2+3] Annulation to Construct Pyrroloquinolines

“…Treatment of compound 3a and phosphorus ylide in CH 3 CN at 80 °C produced 4c in 87% yield. 13 Treatment of 3a with hydroxylamine in n-BuOH at 80 °C for 8 h led to oxime 4d. 14 The corresponding epoxide 4e could be conveniently prepared from 3a and m-CPBA in good yield.…”

“…Next, the trifluoroacetyl group and the isolated double bond were selectively reduced to produce the corresponding 4a and 4b , respectively, in excellent yields. Treatment of compound 3a and phosphorus ylide in CH 3 CN at 80 °C produced 4c in 87% yield . Treatment of 3a with hydroxylamine in n -BuOH at 80 °C for 8 h led to oxime 4d .…”