Rh(II)/Mg(OtBu)2-Catalyzed Tandem One-Pot Synthesis of 1,4-Oxazepines and 1,4-Oxazines from N-Sulfonyl-1,2,3-triazoles and Glycidols.

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(OtBu)2-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 (R2 ≠ H) afforded seven-membered oxazepine derivatives selectively, while unsubstituted glycidols (R2 = 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.

Advances in tandem reactions with organozinc reagents.

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.

Cu(OAc)2-catalyzed tandem Blaise/Pinner-type reaction for one-pot synthesis of pyrimidin-4-ones.

A novel tandem Blaise/Pinner-type reaction for the one-pot synthesis of pyrimidin-4-ones is described. The Blaise reaction intermediate, formed by addition of a Reformatsky reagent to a nitrile, reacted with a second nitrile chemoselectively in the presence of a catalytic amount of Cu(OAc)(2) to afford pyrimidin-4-ones.

Tandem one-pot synthesis of polysubstituted pyridines using the Blaise reaction intermediate and 1,3-enynes.

A tandem one-pot method for the construction of a pyridine moiety with selective control of substitution patterns has been developed through the sequential reactions of nitrile with a Reformatsky reagent and 1,3-enyne involving regio- and chemoselective addition of the Blaise reaction intermediate to 1,3-enyne, followed by isomerization, cyclization, and an aromatization cascade.

One-pot synthesis of 2-pyridones via chemo- and regioselective tandem Blaise reaction of nitriles with propiolates.

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.

Tandem Blaise-alkenylation with unactivated alkynes: one-pot synthesis of alpha-vinylated beta-enaminoesters from nitriles.

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.

An effective and general method for the highly regioselective synthesis of 1-phenylpyrazoles from beta-enaminoketoesters, tandem Blaise-acylation adducts.

An effective and general route for the regioselective synthesis of 1-phenylpyrazoles has been developed from beta-enaminoketoesters prepared by tandem Blaise-acylation. This method is applicable to a very broad range of substrates, generating a diverse set of 3-aryl-5-alkyl, 3-alkyl-5-aryl, 3,5-diaryl, and 3,5-dialkyl substituted pyrazoles regioselectively. The dichotomous regioselective synthesis of isotopically discriminated 3-CD(3)-5-CH(3) and 3-CH(3)-5-CD(3) substituted pyrazoles showcases the power of this protocol.

The first chemoselective tandem acylation of the Blaise reaction intermediate: a novel method for the synthesis of alpha-acyl-beta-enamino esters, key intermediate for pyrazoles.

The Blaise reaction intermediate, a zinc bromide complex of beta-enamino ester, could be activated in situ by addition of a stoichiometric or catalytic amount of n-BuLi to allow chemoselective tandem C2-acylation providing alpha-acyl-beta-enamino esters, which are valuable intermediates for the syntheses of tri- and tetrasubstituted pyrazoles.