Base-catalyzed cascade reaction

Type of reaction C-N bond formation Reaction conditions Toluene, room temperature Synthetic strategy Base-catalyzed cascade reaction Catalyst l,8-Diazabicycl[5.4.0]undec-7-ene (DBU)... 

A new triethylamine-catalyzed cascade reaction of aromatic aldehydes and propiolates was developed to prepare various benzo[ >]furan-based polycyclic aromatics. Interestingly, the chemical outcome of this process depended on the reaction temperature and was selectively tailored by an appropriate choice of experimental conditions <06OL1241>. 

An efficient methodology for the synthesis of 5-carbolines 28 was developed by Cao, Lai, and coworkers. Such methodology is based on a Pd-catalyzed cascade reaction between 2-iodoanilines and N-tosyl-enynamines (2012 OL38). 

See, for instances (a) S. Santra, R R. Andreana, Org. Lett. 2007, 9, 5035-5038. A one-pot, microwave-influenced synthesis of diverse small molecules by multicomponent reaction cascades, (b) M. Presset, Y. Coquerel, J. Rodriguez, Org. Lett. 2009, 11, 5706-5709. Microwave-assisted domino and multi-component reactions with cyclic acyUcetenes expeditious syntheses of oxazinones and oxazindiones. (c) W.-J. Hao, B. Jiang, S.-J. Tu, X.-D. Cao, S.-S. Wu, S. Yan, X.-H. Zhang, Z.-G. Han, F. Shi, Org. Biomol. Chem. 2009, 7,1410-1414. A new mild base-catalyzed Mannich reaction of hetero-arylamines in water highly efficient stereoselective synthesis of 3-aminoketones under microwave heating, (d) P. Nun, J. Martinez, F. Lamaty, Synthesis 2010, 2063-2068. Microwave-assisted neat procedure for the Petasis reaction. 

Based on these experimental results. Hulling and coworkers investigated the mechanism of the imidazolidinone-catalyzed cascade reaction of a,p-unsaturated butyric aldehydes with 2-methylfuran and chlorinated quinone using density functional theory (DFT) calculations [15]. The results gave a better understanding of the effects of the imidazolidinone catalyst core in the enamine- and iminium-mediated steps and explained the enantioselectivity observed from the experiments depicted above. 

M. Yoshida, M. Fujita, T. Ishii, M. Ihara, A novel methodology for the synthesis of cyclic carbonates based on the palladium-catalyzed cascade reaction of 4-methoxycarbonyloxy-2-butyn-l-ols with phenols, involving a novel carbon dioxide elimination-fixation process, J. Am. Chem. Soc. 125 (2003) 4874-4881. 

Bifunctional base/Brpnsted acid-catalyzed cascade reactions in natural product synthesis... 

BIFUNCTIONAL BASE/BR0NSTED ACID-CATALYZED CASCADE REACTIONS... 

Isocyanides have been explored extensively in cascade reactions, due to their unusual reactivities to form multiple bonds in a one-pot manner with remarkable versatility in producing heterocycles. The reaction of isocyanides with Cu(I) in the presence of base could form the a-cuprioisocynanides, which could undergo formal [3+2] cycloaddition with alkynes to form pyrrole rings. Recently it was reported that the a-cuprioisocynanide intermediates occurred in the copper-catalyzed cascade reaction of isocyanides with A/-(2-haloaryl)propiolamides 109 for the synthesis of... 

In 2001, Larock and Tian reported a palladium-catalyzed cascade reaction of aryl halides and 1-aryl-l-aIkynes to synthesize 9-aIkylidene-9/f-fluorenes 167 [66] (Scheme 6.44). Based on the active role of Pd(IV) in organopalladium chemistry, the authors proposed a mechanism involving the formation, transformation, and reductive elimination of Pd(IV) intermediates and aryl C—H bond activation. It is noteworthy that both carbocyclic and heterocyclic aryl iodides, such as pyridine and thiophene, could be introduced in this reaction. Later, Zhao and Larock reported an efficient palladium-catalyzed cascade reaction for the synthesis of substituted carbazoles 169 from A/-(3-iodophenyl)anilines 168 and alkynes [67] (Scheme 6.45). 

TABLE 8.8 One-Pot Reaction Cascades Composed of Acid-Catalyzed Hydrolysis and Base-Catalyzed Henry Reaction"... 

Scheme 5.12 Cascade reactions with acid-and base-catalyzed steps in the same pot [29]. The acids and bases are defined in the text.

This approach was also employed for pyridolT id thienoP -Z pyrimidine derivative 139, which can be prepared according to the following two procedures by the one-pot base-catalyzed reaction of pyrimidinethione 140 with ethyl 4-chloro-acetoacetate or by cascade heterocyclization of pyrimidine 141 (2003IZV2069). 

Base-catalyzed hydration of conjugated carbonyls, followed by retro-aldol fragmentation has been a common strategy for studying the reaction cascade (1-4). The kinetically important step in the base-catalyzed hydration of an alpha/beta unsaturated carbonyl is similar to a nucleophilic substitution reaction at carbon 3. The reaction cascade proceeds rapidly from the conjugated carbonyl through its hydration and subsequent fragmentation. 

Abstract Cascade reactions involving a transition metal-promoted step and a Michael-type addition process have emerged as a powerful tool to construct cyclic and polycyclic structures. In this review, recent advances in this field are presented. The first part is related to cycloaddition reactions based on zwitterionic jr-allylPd complexes. The second part deals with Michael initiated metal-catalyzed cyclofunctionalization reactions of unactivated C C jt-bonds. Parts three and four feature reactions where an initial Michael addition reaction is followed by either a coupling reaction or an electrophilic trapping. Part five is devoted to Michael terminated reactions. 

Abstract Ruthenium holds a prominent position among the efficient transition metals involved in catalytic processes. Molecular ruthenium catalysts are able to perform unique transformations based on a variety of reaction mechanisms. They arise from easy to make complexes with versatile catalytic properties, and are ideal precursors for the performance of successive chemical transformations and catalytic reactions. This review provides examples of catalytic cascade reactions and sequential transformations initiated by ruthenium precursors present from the outset of the reaction and involving a common mechanism, such as in alkene metathesis, or in which the compound formed during the first step is used as a substrate for the second ruthenium-catalyzed reaction. Multimetallic sequential catalytic transformations promoted by ruthenium complexes first, and then by another metal precursor will also be illustrated. 

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