[3 + 3] Cycloaddition of aza-oxyallyl cations with 1,4-dithiane-2,5-diols for the construction of 3-thiomorpholinones

Lewis base-catalyzed cascade [4 + 2]-annulation reaction of N-alkoxy acrylamides and acyl isothiocyanates: facile access to 2-imino-1,3-thiazinone derivatives

A formal [4 + 2]-cycloaddition reaction of N-alkoxy acrylamides and acyl isothiocyanates was developed via a Lewis base-catalyzed cascade aza-nucleophilic addition/thio-Michael addition process under mild conditions. This study provides a facile approach for preparing 2-imino-1,3-thiazinone derivatives in moderate to excellent yields and enriches the field of heterocyclic acrylamide chemistry. The reported method features metal-free reaction conditions, high atom economy, and easy operation. Moreover, the reaction was successfully scaled up and derivatization reactions were successfully performed.

Synthesis of Polycyclic Imidazolidinones via Cascade [3 + 2]-Annulation of β-Oxo-acrylamides with Cyclic N-Sulfonyl Imines

An Et3N-catalyzed cascade [3 + 2]-annulation of β-oxo-acrylamides with cyclic N-sulfonyl ketimines or sulfamate-derived imines is developed under mild reaction conditions, which provides a concise and efficient route to access valuable sultam- or sulfamidate-fused imidazolidinone derivatives in good to excellent yields (80-95% yields) with excellent diastereoselectivities (>20:1 drs). The current protocol features atom economy, a transition-metal-free process, and broad functional group tolerance. Moreover, the asymmetric variant of the [3 + 2]-cycloaddition reaction was achieved in the presence of diphenylethanediamine or quinine-based bifunctional squaramide organocatalysts C-1 and C-11, giving the corresponding chiral polycyclic imidazolidinones in 68-90% yields with 25-94% ees and >20:1 drs in all cases.

Organocatalytic cascade nucleophilic/aza-Michael addition reactions: metal-free catalytic strategy for the synthesis of hydantoins

Lewis base-catalyzed cascade nucleophilic/aza-Michael addition reaction of N-alkoxy β-oxo-acrylamides with isocyanates has been developed to afford various highly functionalized hydantoin derivatives in 80-98% yields under mild reaction conditions. The intriguing features of this method include metal-free reaction conditions, low catalyst loading, broad substrate scope and short reaction time.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Synthesis of spirocyclic oxazole derivatives from 2-arylidene cycloalkanones and α-halohydroxamates

Herein we disclose a facile route to spirocyclic oxazole derivatives via [3 + 2] cycloaddition reactions between 2-arylidene cycloalkanones and azaoxyallyl cations that formed in situ from α-halohydroxamates in the presence of base. This methodology was shown to lead to an efficient formation of a series of functionalized spirocyclic oxazole derivatives in good to excellent yields.