The design and implementation of tandem reactions provides organic chemists with numerous challenges, in particular that of undesired cross-reactivity between substrates. Among organometallics, the use of organozinc reagents in tandem reactions provides several advantages as a result of their broad functional group tolerance and compatibility with transition metals. This review highlights prominent examples of recent advances in tandem reactions with organozinc reagents that illustrate their potential in organic synthesis.
A novel, one-pot route for the synthesis of nonaromatic ring-fused 1,4-oxazepines and 1,4-oxazines has been developed. The reaction features a sequential rhodium(II)-catalyzed reaction of N-sulfonyl-1,2,3-triazoles with glycidols, followed by a regioselective Lewis acid Mg(OBu)-catalyzed intramolecular ring-opening reaction. It has been found that the regioselectivity in the epoxide ring-opening was largely determined by the substituents on the glycidols. Thus, substituted glycidols (R ≠ H) afforded seven-membered oxazepine derivatives selectively, while unsubstituted glycidols (R = H) afforded six-membered oxazine derivatives. Plausible reaction pathways are elucidated and supported by experiments with several glycidols bearing different substituents around the epoxide functionality.
The Blaise reaction intermediate, generated in situ from Reformatsky reagent and nitrile, reacted with propiolates in a chemo- and regioselective manner to afford 2-pyridone derivatives in good to excellent yields.
The in situ generated Blaise reaction intermediate, a zinc bromide complex of beta-enaminoester, reacts with various unactivated terminal alkynes and an internal alkyne under mild conditions to afford alpha-vinylated beta-enaminoesters in good to excellent yields.
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