Organocatalytic enantio- and diastereoselective synthesis of highly substituted δ-lactones via a Michael-cyclization cascade

Diastereo- and Enantioselective Mannich/Cyclization Cascade Reaction Access to Chiral Benzothiazolopyrimidine Derivatives

An efficient asymmetric Mannich/cyclization cascade strategy was established from 2-benzothiazolimines with N-acylpyrazoles to provide optical active benzothiazolopyrimidine derivatives using a copper-based complex. The mild cascade process constructed various structurally diverse products with broad scope of substrates together with excellent enantioselectivities (up to 99 % ee) and diastereoselectivities (up to 99:1 d.r.).

An organocatalytic asymmetric Mannich reaction of pyrazoleamides with cyclic trifluoromethyl ketimines: enantioselective access to dihydroquinazolinone skeletons

A series of trifluoromethyl dihydroquinazolinones were obtained in excellent results via an asymmetric Mannich reaction of pyrazoleamides and cyclic trifluoromethyl ketimines.

Organocatalytic, enantioselective synthesis of benzoxaboroles via Wittig/oxa-Michael reaction Cascade of α-formyl boronic acids

An unprecedented enantioselective synthesis of 3-substituted benzoxaboroles has been developed. An in situ generated ortho-boronic acid containing chalcone provides the chiral benzoxaboroles via an asymmetric oxa-Michael addition of hydroxyl group attached to the boronic acid triggered by the cinchona alkaloid based chiral amino-squaramide catalysts. In general, good yields with good to excellent enantioselectivities (up to 99%) were obtained. The resulting benzoxaboroles were converted to the corresponding chiral β-hydroxy ketones without affecting the enantioselectivity.

Cascade reactions of nitrogen-substituted isocyanates: a new tool in heterocyclic chemistry

In contrast to normal C-substituted isocyanates, nitrogen-substituted isocyanates (N-isocyanates) are rare. Their high reactivity and amphoteric/ambident nature has prevented the scientific community from exploiting their synthetic potential. Recently, we have developed an in situ formation approach using a reversible equilibrium, which allows controlled generation and reactivity of N-isocyanates and prevents the dimerization that is typically observed with these intermediates. This blocked (masked) N-isocyanate approach enables the use of various N-isocyanate precursors to assemble heterocycles possessing the N-N-C[double bond, length as m-dash]O motif, which is often found in agrochemicals and pharmaceuticals. Cascade reactions for the rapid assembly of several valuable 5- and 6-membered heterocycles are reported, including amino-hydantoins, acyl-pyrazoles, acyl-phthalazinones and azauracils. Over 100 different compounds were synthesized using amino-, imino- and amido-substituted N-isocyanates, demonstrating their potential as powerful intermediates in heterocyclic synthesis. Their reactivity also enables access to unprecedented bicyclic derivatives and to substitution patterns of azauracils that are difficult to access using known methods, illustrating that controlled reactivity of N-isocyanates provides new disconnections, and a new tool to assemble complex N-N-C[double bond, length as m-dash]O containing motifs.

Enantioselective Synthesis of Highly Substituted Chromans via the Oxa-Michael-Michael Cascade Reaction with a Bifunctional Organocatalyst

A highly enantioselective synthesis of chiral chroman derivatives via an oxa-Michael-Michael cascade reaction has been developed using a bifunctional thiourea organocatalyst. The products were obtained with excellent enantioselectivities (up to >99%), good yields (up to 95%), and diastereoselectivities (up to 5:1).