Reactivity of 4,6-dioxy-2-pyrones in the Diels-Alder process

The Use of Bis(trimethylsilyl)acetamide and Bis (trimethylsilyl)urea for Protection and as Control Reagents in Synthesis

“…The conversion of glutaconic anhydride into the silylated apyrone [Scheme 11] was achieved in very high yield using BSA. 42 The product is a very useful Diels-Alder diene. A new route to oxyallyl cations involves a combination of BSA and a zinc copper couple in benzene.…”

Methods for pyranoannulation: an approach to a new class of polyethers

“…To append a third ring to 6b (X = OH), the lactol was oxidized to lactone, and this intermediate was reacted with the Grignard reagent 9 prepared from 3bromopropionaldehyde ethylene acetal (method b). The new lactol was dehydrated through its mesylate, 10 and the resulting dihydropyran 12 was hydroborated and oxidized to afford an alcohol as nearly a single stereoisomer (Scheme IV). On treatment with thiophenol and acid, the tricyclic material 13 was obtained (anomeric mixture, ratio 6:1).…”

Regioselective Synthesis of Highly Substituted Aromatic Sulfides via Carbonyl−Alkyne Exchange Reaction

“…The carbonyl−alkyne exchange (CAE) reaction − of 2,2-dialkyl-2,3-dihydro-4 H -pyran-4-ones 1 with electron-deficient acetylenes 2 , yielding protected phenols 3 (Scheme ), which has been studied previously in our group, constitutes a novel approach for the regioselective de novo construction of highly functionalized aromatic compounds. Thus, in situ transformation of dihydropyranones 1 into their corresponding silyl enol ethers 4 and [4+2] cycloaddition with acetylenes 2 yieldedvia bicyclic intermediates 5 and electrocyclic extrusion of acetonethe protected phenols 3 in good to excellent yields (Scheme ).…”