Diazo compounds are remarkably versatile metal carbene precursors which participate in metal-catalyzed rearrangements, cycloadditions, XÀH (X = C, N, O, Si, S, etc.) bond insertions, and ylide-forming reactions with concomitant expulsion of N 2 . [1] These compounds also take part in 1,3dipolar cycloaddition reactions of a wide range of dipolarophiles with retention of the CN 2 moiety. [2] Because of their unique properties and extensive applications, the interest in the chemistry of diazo compounds has been long standing. [1e, 3] However, efficient synthesis of chiral diazo compounds, especially those with delicate functionalities, is still in urgent need. [4] Enantioselective C À C bond formation employing diazo esters as nucleophilic reaction partners provides a straightforward approach to chiral diazo compounds. [5] Nevertheless, the instability of the diazo moiety to transition metals [1,6] renders them unmanageable in organometallic catalysis, and the nature of the esters makes them less reactive in organocatalysis. [7,8] Until now, the described successful examples are focused on aldol [8,9] /Mannich-type [10] reactions under the catalysis of chiral zirconium, [9a] magnesium, [8a] scandium, [9b] and zinc [9c] complexes or chiral Brønsted acids with simple electrophiles, such as carbonyl compounds and imines (Scheme 1 a,b). Exploitation of diazo esters as nucleophiles in asymmetric catalysis remains a significant challenge.Recently, chiral Lewis bases were used to catalyze asymmetric allylic alkylation, with Morita-Baylis-Hillman (MBH) adducts as electrophiles, through a S N 2'/S N 2' cascade and has emerged as a powerful strategy for the construction of multifunctional compounds. [11] To expand the number of reactions using diazo esters as nucleophiles, and also in . Keywords: diazocompounds· fluorine · heterocycles · organocatalysis synthetic methods Scheme 5. The synthesis of optically pure N Heterocycles derived from the chiral a-allylic diazo esters 4. DMAP = 4-(dimethylamino)pyridine, Ts = 4-toluenesulfonyl. Scheme 4. Gram-scale reaction for the preparation of the optically pure a-allylic diazo esters 4. Scheme 6. PMP = para-methoxyphenyl. Angewandte Chemie 6291

A straightforward and efficient protocol for the construction of structurally and biologically interesting chiral flavanoids incorporating three privileged structures, i.e., chromanone, dihydropyran, and indole, has been developed on the basis of chiral bifunctional tertiary amine thiourea-catalyzed asymmetric inverse-electron-demand Diels-Alder reaction of chromone heterodienes and 3-vinylindoles, which were used as dienophiles.

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Carbon-carbon bond formation: A highly efficient method for the oxo-hetero-Diels-Alder reaction of 2-oxoindolin-3-ylidenes based on chiral calcium phosphate is described. In general, adducts were obtained with high yields and excellent diastereo- and enantioselectivities (up to 96 % yield, >99:1 endo/exo, >99 % ee; see scheme, Boc = tert-butoxycarbonyl).

Anything between ureas? Spiro[isoxazolidine-3,3'-oxindole]s have been constructed by employing methyleneindolinones and nitrones as the starting materials through [3+2] annulation catalyzed by a bisthiourea. Products with three contiguous stereocenters, including one spiroquaternary stereocenter, are obtained in good yields with excellent enantio- and diastereoselectivity. The bisthiourea catalyst acts as a multiple-hydrogen-bond donor to simultaneously activate both substrates.