Gold-Catalyzed 1,3-Addition of a sp<sup>3</sup>-Hybridized C−H Bond to Alkenylcarbenoid Intermediate

Bhunia, Sabyasachi; Liu, Rai‐Shung

doi:10.1021/ja807384a

Cited by 142 publications

(53 citation statements)

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“…We have recently reported a formal [4+2] approach for the synthesis of piperidin-4-ones [13] via a key gold catalysis [14][15][16][17][18][19][20][21][22][23]. In this two-step sequence (Scheme 1), a secondary amine is initially alkylated with but-3-ynyl tosy late in a S N 2 reaction; subsequent m-CPBA oxidation of the formed tertiary amine into the corresponding N-oxide is followed by Au(I)-catalyzed intramolecular oxidation of the alkyne moiety, yielding an -oxo gold carbene intermediate (i.e., A); a formal carbene insertion into the CH bond  to the nitrogen atom presumably via sequential hydride migration and cyclization leads to an overall 4+2 annulation between a secondary amine (a C1 + N1 unit) and a but-3-ynyl moiety (a C4 unit).…”

Section: Introductionmentioning

confidence: 99%

Total synthesis of (+)-lentiginosine via a key Au catalysis

Cui

Zhang

2010

Sci. China Chem.

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Section: Introductionmentioning

confidence: 99%

Total synthesis of (+)-lentiginosine via a key Au catalysis

Cui

Zhang

2010

Sci. China Chem.

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“…Recently, special attention has been paid to Pt- [8] and Au-catalyzed [9] intramolecular coupling between terminal unactivated alkynes and C sp 3 À H bonds in alkynyl ethers and amines to produce complex spiro or fused bicyclic systems by a tandem 1,5-hydride shift/cyclization sequence. [10] The above methods require temperatures as high as 100-120 8C to achieve good results and under Pt catalysis only 5-exo methylene bicyclic structures are formed. We report herein a mild procedure based on a novel tandem Ru-catalyzed carbene addition to terminal alkynes/insertion into C sp 3 À H bonds in alkynyl acetals, ethers, and amines to form complex spiro and fused bicyclic structures by 1,5-and 1,6-hydride shift/cyclization sequences (Scheme 1).…”

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confidence: 99%

Cyclization by Catalytic Ruthenium Carbene Insertion into CH Bonds

et al. 2011

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Novel reactions that can selectively functionalize carbon À hydrogen bonds are very important because they offer new strategic approaches in synthesis.[1] A remarkable method for such CÀH functionalization involves the insertion of metal carbenes into CÀH bonds.[2] The regioselectivity of these CÀH insertions is governed by electronic, steric, and conformational factors.[3] Typically, in nonconstrained systems, metalcatalyzed intramolecular C À H insertion reactions predominantly afford five-membered rings (1,5-insertions). [2,4] The formation of smaller and larger rings is achieved only when geometrical constraints or activated CÀH bonds are involved.[5] Usually, Rh- [6] and Cu-catalyzed [7] CÀH insertions have shown amazing versatility in both intramolecular and intermolecular reactions, but it is still a challenging goal to discover other metals and tethers that facilitate the construction of rings by C sp 3 ÀH functionalization. Recently, special attention has been paid to Pt- [8] and Au-catalyzed [9] intramolecular coupling between terminal unactivated alkynes and C sp 3 À H bonds in alkynyl ethers and amines to produce complex spiro or fused bicyclic systems by a tandem 1,5-hydride shift/cyclization sequence.[10] The above methods require temperatures as high as 100-120 8C to achieve good results and under Pt catalysis only 5-exo methylene bicyclic structures are formed. We report herein a mild procedure based on a novel tandem Ru-catalyzed carbene addition to terminal alkynes/insertion into C sp 3 À H bonds in alkynyl acetals, ethers, and amines to form complex spiro and fused bicyclic structures by 1,5-and 1,6-hydride shift/cyclization sequences (Scheme 1).[11]The cyclization of dioxolane 1 a was the first reaction examined under a variety of catalytic conditions (Table 1). After some preliminary experiments, [12] the well-known conditions, established by Dixneuf and co-workers, for the preparation of Ru carbenes starting from alkynes were employed.[13] Thus, a 1,5-hydride shift/cyclization sequence gave the functionalized spiro [5,5] compound 2 a in a moderate yield of 40 % and the linear hydroxyester 3 a as the major isolated product in 50 % yield, by stirring a dioxane solution of 1 a (0.15 m) with 1 equivalent of N 2 CHTMS (2 m in hexanes) and 10 mol % of [Cp*Ru(cod)Cl] as catalyst at 60 8C (Table 1, entry 1). A lower overall yield and a similar ratio of 2 a and 3 a were obtained when the reaction was performed in dioxane at room temperature (Table 1, entry 2). Gratifyingly, the desired spiro compound 2 a or its desilylated analogue 2 a' [13e,g] were isolated in fairly good yields (66-80 %) when the reactions were carried out in either diethyl ether or MeOH at room temperature (Table 1, entries 3 and 4). [14] However, other typical solvents like THF and toluene gave either lower yields and/or longer reaction times (Table 1, entries 5 and 6).

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“…Enynes 25c-d react with catalyst A gave 32a-c and 33a-c by 1,5-migration followed by a formal C-H insertion (Scheme 7). Related formal C-H insertions have been observed in other reaction proceeding through Au or Pt carbenes [83][84][85][86][87][88][89][90]. These results are consistent with a mechanism in which the intermediate a,b-unsaturated gold carbene/allyl-gold cation 34 abstracts a hydride from the ArCH 2 O group to form a g 1 -allyl-gold(I) 35, which reacts at C-1 or C-3 with the oxonium cation to give 32a-c or 33a-c, respectively.…”

Section: Gold-catalyzed Cyclization Of Simple 16-enynesmentioning

confidence: 67%

Complexity via Gold-Catalyzed Molecular Gymnastics

Echavarren

Jiménez‐Núñez

2010

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Reactions of 1,6-enynes catalyzed by gold(I) complexes usually proceed stereospecifically through highly distorted cyclopropyl gold carbenes. Substrates with an alkoxy substituent at the propargylic position undergo stereoselective transformations through intermediates in which the OR group and the gold carbene are anti-oriented. Intramolecular attack of carbonyl groups to the cyclopropyl gold carbene is faster than the 1,5-migration of the OR groups, which itself is faster than the intramolecular cyclopropanation by a pendant alkenyl group. The intramolecular attack of carbonyl groups is the key transformation in the [2?2?2] gold-catalyzed cycloaddition, which has been applied in the total synthesis of (?)-orientalol F.Electrophilic metals catalyze the cyclization of 1,n-enynes to give a variety of cyclic structures (recent reviews in [1-4]) [5][6][7][8][9][10][11][12][13][14][15][16]. In the absence of nucleophiles, simple 1,6-enynes 1 undergo skeletal rearrangement to give products 2 (single exo-cleavage) and 3 (double exo-cleavage) ( Fig. 1) . In a third type skeletal rearrangement, dienes 4 (single endo-cleavage) were found using cationic Au(I) catalysts [5,38]. Products of type 4 were later found in reactions catalyzed by InCl 3 [27, 28], Fe(III) [6], or Ru(II) [39]. Cyclobutenes resulting from a [2?2] cycloaddition process have also been obtained from 1,6-[40], 1,7-[25, 29-31, 34, 41], and 1,8-enynes [42, 43]. Other type of cyclobutenes have been obtained in the palladium-[17, 18], platinum-[44], and gold-catalyzed cyclization of enynes [15,16,[45][46][47].Although dienes 2 obtained by the single exo-cleavage are identical to those formed by the metal-catalyzed metathesis of enynes [48,49], the mechanism of the skeletal rearrangement is very different [50,51]. For Au(I), the rearrangement was proposed to proceed via intermediates 5 (Fig. 2) [52]. On the other hand, the double-cleavage skeletal rearrangement usually leads to dienes 3 with predominant [1-4, 17-21, 38], or exclusive Z [53, 54] configuration. For Au(I), products of type 3 are obtained via rearranged carbene 6, followed by 1,2-H shift and protodemetalation [52]. Experimental support for the involvement of 6 has been obtained in reactions in which these intermediates have been trapped with alkenes [55], indoles, allyl silanes [56][57][58], and carbonyl compounds [59,60]. Proton loss from 6 can form 1,4-dienes in InCl 3 -catalyzed reactions of substrate in which R 0 is an alkyl group [27].The dual character of intermediates 5 as metal carbenes and carbocationic species has been recently discussed [1][2][3][4][61][62][63]. Conventionally, these complexes are often depicted as cyclopropyl gold carbenes 5, although DFT calculations show that these species have highly distorted structures, intermediate between cyclopropyl gold carbenes and gold-stabilized homoallylic carbocations [38,52]. A gold carbene has been formed in the gas phase, see [64,65]. Intermediates of type 5 are involved in other processes such as nucleophilic additions of heteronucleo...

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Gold-Catalyzed 1,3-Addition of a sp³-Hybridized C−H Bond to Alkenylcarbenoid Intermediate

Cited by 142 publications

References 20 publications

Total synthesis of (+)-lentiginosine via a key Au catalysis

Total synthesis of (+)-lentiginosine via a key Au catalysis

Cyclization by Catalytic Ruthenium Carbene Insertion into CH Bonds

Complexity via Gold-Catalyzed Molecular Gymnastics

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Gold-Catalyzed 1,3-Addition of a sp3-Hybridized C−H Bond to Alkenylcarbenoid Intermediate

Cited by 142 publications

References 20 publications

Total synthesis of (+)-lentiginosine via a key Au catalysis

Total synthesis of (+)-lentiginosine via a key Au catalysis

Cyclization by Catalytic Ruthenium Carbene Insertion into CH Bonds

Complexity via Gold-Catalyzed Molecular Gymnastics

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Gold-Catalyzed 1,3-Addition of a sp³-Hybridized C−H Bond to Alkenylcarbenoid Intermediate