The Lewis acid mediated Nicholas reaction of potassium alkynyltrifluoroborates and propargyl acetate-hexacarbonyldicobalt complexes affords 1,4-diyne dicobalt hexacarbonyl complexes in good yields. The analogous Nicholas reactions of potassium alkenyltrifluoroborates give 1,3-enyne dicobalt hexacarbonyl complexes in most cases, although the initial site of reaction can vary. Potassium vinyltrifluoroborate itself affords alkynylcyclopropane complexes.
AbstractCarbohydrates, in the form of chitin, chitosan and cellulose, are one of the most available, renewable, and sustainable chemical feedstocks. Their conversion to biofuels, fine chemicals, and industrially-relevant monomers is becoming increasingly viable and promising as innovation decreases the price of this technology, and climate change and the price of fossil fuels increases the social and economic costs of using traditional feedstocks. In recent years, carbohydrates have been increasingly used as sources for nitrogen-containing fine chemicals. This chapter, with 86 references, provides a brief overview of the conversion of carbohydrate biomass to the standard hydrocarbon and oxygen-containing derivatives, and then provides a survey of recent progress in converting the biopolymers, and the derived mono and di-saccharides, into nitrogen-containing molecules with a special focus on N-heterocycle synthesis for medicinal applications.
The Lewis acid-mediated Nicholas
reactions of propargyl acetate–Co2(CO)6 complexes with a series of potassium alkynyltrifluoroborates
and potassium alkenyltrifluoroborates are described. Alkynyltrifluoroborates
directly alkynylate the intermediate propargyldicobalt cations. In
contrast, alkenyltrifluoroborates proceed through one of the three
modes of dominant reactivity: C-2-substituted alkenyltrifluorobrates
directly alkenylate, predominantly with the retention of stereochemistry.
C-1-substituted alkenyltrifluoroborates alkenylate at C-2. Potassium
vinyltrifluoroborate incorporates a cyclopropane at the site propargyl
to alkynedicobalt. Computational analysis of these systems explains
the differential modes of reactivity of alkenyltrifluoroborates and
outlines the probable mechanisms for the formation of each product.
The γ- carbonyl cations generated from propargyl ether-(Co2CO)6 complexes undergo intramolecular Nicholas reactions to give dehydrobenzoxacin-3-one-Co2(CO)6 complexes in good yields. Reductive decomplexation and subsequent manipulation allows the synthesis of (±)-heliannuol...
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