Xing-Zhong Shu

Selective Functionalization of sp3 C−H Bonds Adjacent to Nitrogen Using (Diacetoxyiodo)benzene (DIB)

A PhI(OAc)(2) mediated selective functionalization of sp(3) C-H bonds adjacent to a nitrogen atom has been reported. When piperidine derivates were used, direct diacetoxylation of alpha and beta sp(3) C-H adjacent to a nitrogen atom were observed to afford various cis-2,3-diacetoxylated piperidines. On the other hand, tetrahydroisoquinoline derivatives gave various alpha-C-H functionalized products in the presence of PhI(OAc)(2). Nitroalkanes, dialkyl malonates, and beta-keto ester are active participants in this coupling reaction. Meanwhile, alpha-amino nitriles can also be obtained by oxidative coupling of amines with malononitrile.

Synthesis of Isoquinoline Derivatives via Ag-Catalyzed Cyclization of 2-Alkynyl Benzyl Azides

Ag-catalyzed cyclization of 2-alkynyl benzyl azides offers a novel and efficient method for the synthesis of substituted isoquinoline. The reaction proceeds smoothly in moderate to good yields and tolerates considerable functional groups. The reaction conditions and the scope of the process are examined, and a plausible mechanism is proposed.

Platinum-catalyzed cross-dehydrogenative coupling reaction in the absence of oxidant

A third strategy for cross-dehydrogenative coupling reaction has been reported via platinum-catalyzed sp(3) C-H and sp(3) C-H coupling reaction in the absence of oxidant. Nitroalkanes as well as dialkyl malonate derivatives, beta-keto esters and malononitrile are active participants in this coupling reaction. Both cyclic and acyclic non-activated simple ketones are good reactants in this reaction.

Platinum-Catalyzed Michael Addition and Cyclization of Tertiary Amines with Nitroolefins by Dehydrogenation of α,β-sp3 C−H Bonds

A mild platinum-catalyzed oxidative dehydrogenation of alpha,beta-C(sp(3))-H bonds of tertiary amines in the presence of ambient oxygen is revealed, and the in situ formed enamines subsequently reacting with various nitroolefins resulted in the development of two one-pot synthetic protocols involving Michael addition-elimination and Michael addition-cyclization. By using different functionalized nitroolefins compatible with the current oxidative conditions, two types of structurally divergent products, trisubstituted enamines and chromano[2,3-b]piperidines, could be expediently accessed, respectively.

Au-catalyzed tandem cyclization/[1,2]-alkyl migration reaction of epoxy alkynes: synthesis of spiropyranones.

A novel gold-catalyzed tandem cyclization/[1,2]-alkyl migration process of epoxy alkynes to spiropyranones has been discovered. From this process, the construction of adjacent multiple stereocenters with a new quaternary carbon atom is achieved. The gold-catalyzed domino process is stereospecific with respect to the migrating carbon atom. A type of unusual C-C bond cleavage of epoxide systems has also been discovered, which can lead to the formation of two Z alkenes and a carbonyl functional group in one step with excellent stereoselectivity. Furthermore, this efficient domino process could be achieved in the presence of the simplest and least expensive gold catalyst [NaAuCl(4)].2H(2)O with a low catalyst loading.

PtCl2-catalyzed tandem triple migration reaction toward (Z)-1,5-dien-2-yl esters.

A novel method for the selective synthesis of (Z)-1,5-dien-2-yl esters has been developed though Pt(II)-catalyzed tandem 1,2-acyl and 1,2-hydride migration, along with an allyl migration reaction of propargylic carboxylates with electronically unbiased internal alkynes. The unusual selectivity of 1,2-acyloxy migration was realized.

Platinum-Catalyzed Cycloisomerization Reaction of 1,6-Enyne Coupling with Rearrangement of Propargylic Esters

A platinum-catalyzed cycloisomerization of 1,6-enyne coupling with the rearrangement chemistry of propargylic ester has been developed. Most probably, under platinum catalysis, propargylic ester undergoes the 1,3-acyloxy migration to afford metal allene intermediate, which is followed by the Diels-Alder-type reaction. 1,3-Acyloxy migration is the key step during the transformation.

Synthesis of Naphthalenyl Acetate by Platinum‐Catalyzed [1,5]‐Sigmatropic Hydrogen Shift of Propargylic Esters

The [1,5]-sigmatropic hydrogen shift is a useful tool in organic synthesis which has stimulated many mechanistic studies and has found numerous applications in complex molecules synthesis. In cyclic systems, this process has also been proved efficiently by using acyclic dienes and its derivates, such as cis-1,3-dienes, cis-1-alkyl-2-vinylcyclopropanes and cis-1-allen-4-enes [Eq. (1–3)]. However, in the alkyne area this reaction mechanism has not been observed until Liu and co-workers recently reported that cis-3-en-1-ynes did undergo the [1,5]-sigmatropic hydrogen shift via ruthenium–vinylidene intermediates [Eq. (4)]. Consequently, reactions of the [1,5]-hydrogen shift in the alkyne chemistry are still largely unexplored. As a special of alkynes, readily available propargylic esters have continued to attract the interest of different research groups. The metal–allene complexes, which are formed during the reaction, are considered common intermediates, that further react with various functional groups resulting in astonishingly diverse products under platinum and gold catalysis. We envisioned that this type of allenyl esters B could realize the [1,5]-hydrogen shift process, although the nucleophilic attack on the C2 position still remains virtually unknown compared with C1 and C3 positions [Eq. (5)]. Herein, we report the first examples of [1,5]-sigmatropic hydrogen shift reaction of propargylic esters. Optimization studies of this transformation began with propargylic ester 1 a (0.3 mmol) with various catalysts. Among the platinum catalysts used (Table 1, entries 1–4), PtCl2 (10 mol %) with CO (1 atm) gave the best result (Table 1, entry 4). Low-catalyst loading led to the poor yield of 2 a, whereas a similar result was obtained when 20 mol % of PtCl2 were added (Table 1, entries 5 and 6). The changes in solvent and temperature did not give better results (Table 1, entries 7–10). Gold catalysts could also catalyze this cyclization, however, no superior results were obtained (entries 11–14). Thus, the use of PtCl2 (10 mol %) and CO (1 atm) in toluene (2 mL) at 85 8C was found to be most efficient, which was subsequently used as the standard reaction condition. Under these optimal conditions, we studied the scope of this cyclization as shown in Table 2. Besides the phenyl group, various aryl substituents were tolerated at the propargylic position (entries 1–4). The vinyl group also gave moderate yields of 2 e (entry 5). When the furyl substituent was used, uneliminated product 3 a was isolated in 81 % yield [a] Dr. X.-Z. Shu, K.-G. Ji, S.-C. Zhao, Z.-J. Zheng, J. Chen, L. Lu, X.-Y. Liu, Prof. Dr. Y.-M. Liang State Key Laboratory of Applied Organic Chemistry Lanzhou University Lanzhou 730000 (China) Fax: (+86) 931-8912582 E-mail : liangym@lzu.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200801591.

Novel Carbon−Carbon Bond Formation from Propargylic Alcohols and Olefin toward Five-Membered Heterocyclic Rings Catalyzed by AgSbF6

A mild and direct process for C-C bond formation from propargylic alcohols and olefin has been developed in the presence of a silver catalyst. In this reaction, trace amounts of water were necessary and allene alcohols 2 and 1,3-dienes 3 were obtained selectively.

Gold-catalyzed tandem cyclization/Friedel–Crafts type reactions toward furan derivatives

A simple and convenient synthetic approach to furan derivatives 4 has been developed via gold-catalyzed tandem cyclization/Friedel-Crafts type reactions.