2-aza-1,3-dienes: Methods of synthesis and stereochemical studies

An Ab Initio Study of Substituent Effects on the Electrocyclization of Silyloxyazadienes

“…[2] These compounds, usually synthesized by the reaction of silylimines with ketenes, are stable and, following the Staudinger approach, [3] have been used to obtain β-lactams through an electrocyclic ring closure reaction. [4] However, two problems have to be taken into account: (1) With silylimines and ketenes bearing alkyl groups or no substituent at all, very stable azadienes are formed and, under the standard experimental conditions, no spontaneous electrocyclic ring closure to β-lactams is observed. [5] (2) Ring closure to trans β-lactams is generally achieved under reflux conditions, but with ketenes substituted by an alkoxy or an amino group, a spontaneous ring closure to cis β-lactams, at room temperature, is observed.…”

“…[1] In this context, the use of 3-trialkylsilyloxy-2-aza-1,3-dienes was shown to be particularly attractive. [2] These compounds, usually synthesized by the reaction of silylimines with ketenes, are stable and, following the Staudinger approach, [3] have been used to obtain β-lactams through an electrocyclic ring closure reaction.…”

Synthesis of enantiomerically pure (S)- and (R)-fluoxetine (Prozac®) via a hetero Diels–Alder strategy

“…[14][15][16][17][18] Reaction of diene 1 with benzaldehyde under BF 3 -etherate mediated reaction conditions, gave rise to four isomeric products 2, 3, 4 and 5 in 82% combined yields (Scheme 1). Flash chromatography of the crude reaction mixture allowed the separation of the two couples of diastereomeric Diels-Alder adducts: the adducts 2 and 3 and the adducts 4 and 5 (Scheme 1).…”

A Hetero Diels–Alder Concerted vs. Aldol Stepwise Mechanism in the Cyclization of Silyloxyazadienes with Aldehydes: A Theoretical Study

“…[2] The reaction with aldehydes gives rise to tetrahydrooxazinones with various substitution patterns (Scheme 1) and takes place in neutral conditions [3] or in presence of a stoichiometric amount of boron trifluoride etherate.…”