Chiral Spiro Catalysts. In: Ma S, editor. Asymmetric Catalysis from a Chinese Perspective. Berlin: Springer Berlin Heidelberg; 2011. pp. 1-28. [DOI: 10.1007/978-3-642-19472-6_1]

The Co(ii)/spiroBox-catalyzed enantioselective Mukaiyama-Mannich reaction for the synthesis of quaternary α-amino acid derivatives

Co(ii)/spiroBox-catalyzed Mukaiyama-Mannich reactions of enol silyl ethers with cyclic N-sulfonyl ketimino esters were examined and showed excellent yields and enantioselectivity values.

Synthesis and Evaluation of C2-Symmetric SPIROL-Based bis-Oxazoline Ligands

This communication describes the synthesis of new bis-oxazoline chiral ligands (SPIROX) derived from the C2-symmetric spirocyclic scaffold (SPIROL). The readily available (R,R,R)-SPIROL (2) previously developed by our group was subjected to a three-step sequence that provided key diacid intermediate (R,R,R)-7 in 75% yield. This intermediate was subsequently coupled with (R)- and (S)-phenylglycinols to provide diastereomeric products, the cyclization of which led to two diastereomeric SPIROX ligands (R,R,R,R,R)-3a and (R,R,R,S,S)-3b in 85% and 79% yield, respectively. The complexation of (R,R,R,R,R)-3a and (R,R,R,S,S)-3b with CuCl and Cu(OTf)2 resulted in active catalysts that promoted the asymmetric reaction of α-diazopropionate and phenol. The resultant O–H insertion product was formed in 88% yield, and with excellent selectivity (97% ee) when ligand (R,R,R,R,R)-3a was used.

Rhodium(iii)-catalyzed asymmetric [4+1] spiroannulations of O-pivaloyl oximes with α-diazo compounds

Chiral Rh^III catalysts can catalyze the asymmetric [4+1] spiroannulation of O-pivaloyl oximes with α-diazo homophthalimides under redox-neutral and acid/base-neutral conditions, leading to formation of chiral spirocyclic imines as a result of C-H activation and N-O cleavage. The reaction proceeded with high efficiency and features broad substrate scope, mild reaction conditions, and high to excellent enantioselectivities.

Recent quinone diazide based transformations via metal–carbene formation

Recent advancements in versatile synthetic transformations using quinone diazide based metal carbenes have been summarized.

Development of a C2-Symmetric Chiral aza Spirocyclic Diol

A C₂-symmetric chiral spirocyclic diol aza-SPINOL containing a spirooxindole scaffold has been designed, synthesized, and optically resolved. The product could be synthesized on gram scale in an overall yield of 22%. Moreover, elaborations of aza-SPINOL to other chiral ligands as well as the preliminary investigation of the related bisphosphine ligand in the desymmetrization of bisallylic amide were reported.

[4 + 1] annulation reaction of cyclic pyridinium ylides with in situ generated azoalkenes for the construction of spirocyclic skeletons

Two new types of cyclic pyridinium ylides were designed and further used in reactions with azoalkenes to access structurally diverse spirocyclic compounds. A range of spiropyrazoline oxindoles could be smoothly obtained in up to 99% yield via a [4 + 1] annulation process with oxindole 3-pyridinium ylides as C1 synthons. Similarly, a series of spiropyrazoline indanones could be prepared with indanone 2-pyridinium ylides as C1 synthons. This work represents the first example of cyclic pyridinium ylides as C1 synthons for the efficient construction of spirocyclic compounds.

Studies on the formal [3 + 2] cycloaddition of aziridines with alkenes for the synthesis of 1-azaspiroalkanes

The Lewis acid-mediated [3 + 2] cycloaddition of N-sulfonyl- and N-sulfamoylaziridines with alkenes provides a rapid and efficient access to 1-azaspiro[4.n]alkanes. Experimental studies have been combined with DFT calculations to explore the mechanism of the reaction. They demonstrate that the nature of the electron-withdrawing nitrogen protecting group has a very limited influence on the course of the reaction and, particularly, on the initial formation of the 1,3-zwitterionic species through C-N bond cleavage, which has been found to be the rate-determining step. Compared to N-sulfonylaziridines, N-sulfamoylaziridines have proved to be more synthetically useful synthons that afford crystalline polycyclic structures in good yields. A short sequence of catalytic C(sp(3))-H amination-cyclization-[3 + 2] cycloaddition has then been successfully designed to afford the homologue 1-azaspiro[5.n]alkanes, thereby illustrating the higher versatility of sulfamates in these cycloadditions.