Aza-Baylis–Hillman reaction

<p>The aza-Baylis–Hillman reaction or aza-BH reaction in <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a> is a variation of the <a href="/facts/Baylis%E2%80%93Hillman_reaction/F8hfP4tR">Baylis–Hillman reaction</a> and describes the reaction of an electron deficient <a href="/facts/Alkene/RtYcS6kU">alkene</a>, usually an <a href="/facts/%CE%91,%CE%B2-unsaturated_carbonyl_compound/gAflh5z4">α,β-unsaturated carbonyl compound</a>, with an <a href="/facts/Imine/yK72z07j">imine</a> in the presence of a <a href="/facts/Nucleophile/xYccoaJQ">nucleophile</a>. The reaction product is an <a href="/facts/Allyl/CDxPwyvF">allylic</a> <a href="/facts/Amine/JvfYJfP6">amine</a>. The reaction can be carried out in <a href="/facts/Enantiomeric_excess/TJlYl4gn">enantiomeric excess</a> of up to 90% with the aid of bifunctional <a href="/facts/Chirality_(chemistry)/p5a9pftB">chiral</a> <a href="/facts/Binol/Mkmm6zub">BINOL</a> and <a href="/facts/BINAP/aENgvrs3">phosphinyl BINOL</a> compounds, for example in the reaction of n-(4-chloro-benzylidene)-benzenesulfonamide with <a href="/facts/Methyl_vinyl_ketone/wData1cm">methyl vinyl ketone</a> (MVK) in cyclopentyl methyl ether and <a href="/facts/Toluene/Pzdt8dwD">toluene</a> at -15°C.
</p><p>In one study a <a href="/facts/Reaction_mechanism/9lanyVuy">reaction mechanism</a> for a specific aza-BH reaction is proposed. Given a set of reaction conditions the reaction is found to be <a href="/facts/Order_of_reaction/VK18zUhN">first-order</a> in the <a href="/facts/Triphenylphosphine/nYFNCVcJ">triphenylphosphine</a> nucleophile, MVK and the tosylimine concentration in the <a href="/facts/Rate_determining_step/UC0TNxtX">rate determining step</a> in the presence of a <a href="/facts/Br%C3%B8nsted_acid/bqxQnJoX">Brønsted acid</a> such as <a href="/facts/Phenol/ACJs5NIU">phenol</a> or <a href="/facts/Benzoic_acid/7HrmrBYS">benzoic acid</a>. The presence of an acid facilitates the <a href="/facts/Elimination_reaction/7LSBwU3P">elimination reaction</a> in the <a href="/facts/Zwitterion/P6PzHHcS">zwitterion</a> by proton transfer which becomes much faster and no longer rate determining. A 6 membered cyclic <a href="/facts/Transition_state/34PsdqRd">transition state</a> is proposed for this reaction step. Because this step is also <a href="/facts/Reversible_reaction/V3Afejgb">reversible</a> the presence of acid causes a <a href="/facts/Racemisation/t4C1SIXQ">racemisation</a> process simply by mixing chiral aza-BH adduct, phosphine and acid.   
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Aza-Baylis–Hillman reaction open-in-new

Aza-Baylis–Hillman reaction