Intramolecular reaction

About: Intramolecular reaction is a research topic. Over the lifetime, 5015 publications have been published within this topic receiving 138213 citations.

Olefin Metathesis in Cyclic Ether Formation. Direct Conversion of Olefinic Esters to Cyclic Enol Ethers with Tebbe-Type Reagents

Abstract: Department of Chemistry, The Scripps Research Institute 10666 North Torrey Pines Road, La Jolla, California 92037 Department of Chemistry and Biochemistry UniVersity of California, San Diego 9500 Gilman DriVe, La Jolla, California 92093 ReceiVed October 17, 1995 The olefin metathesis reaction1 is rapidly emerging as a powerful tool in organic synthesis.2 Of particular interest are ring forming metathesis reactions catalyzed by transition metal complexes, several elegant examples of which have recently appeared.3 Despite the successes of this general approach to ring construction, much remains to be improved in terms of scope, convenience, and generality. In this communication we report a new strategy, based on the olefin metathesis reaction, for the generation of cyclic enol ethers directly from olefin esters4 using the Tebbe5 or the Petasis reagents.6 Scheme 1 shows the general concept7 for the envisioned Tebbe-reagent-mediated transformation of olefinic esters of type I to cyclic enol ethers of type VI. Thus it was anticipated that the initially formed enol ether II would react with a second molecule of the Tebbe reagent to afford the titanacyclobutane III, fragmentation of which would then lead to titanium alkylidene IV. Intramolecular reaction of IV was then expected to lead to titanacyclobutane V, whose regioselective fragmentation as shown should allow an entry to the desired cyclic enol ethers VI via olefin metathesis. Implementation of this strategy using olefinic ester 1 leads to the formation of cyclic enol ether 3 via the initially formed methylenation product 2 in 71% overall yield (Scheme 2). The intermediacy of compound 2 was proven by isolation and full spectral characterization followed by conversion to 3 under the influence of the Tebbe reagent. The generality and scope of this new process was investigated by employing a variety of substrates. As illustrated in Table 1, the reaction can deliver a series of sixand seven-membered cyclic enol ethers in good yields (entries 1-3 and 10-12, respectively). In addition to these findings, the important observation of the open-chain products shown in entries 6-9 (Table 1) was made. These hydroxy exomethylenic compounds are presumably obtained by sequential hydrolysis and olefination of the initially formed cyclic enol ethers.8 Apparently the lability of the enol ether products depends on their precise environment and the reaction conditions, a circumstance that

Platinum-Catalyzed Intramolecular Alkylation of Indoles with Unactivated Olefins

Abstract: Reaction of 1-methy-2-(4-pentenyl)indole (1) with a catalytic amount of PtCl2 (2 mol %) in dioxane that contained a trace of HCl (5 mol %) at 60 °C for 24 h led to the isolation of 4,9-dimethyl-2,3,4,9-tetrahydro-1H-carbazole (2) in 92% yield. Platinum-catalyzed cyclization of 2-(4-pentenyl)indoles tolerated substitution at each position of the 4-pentenyl chain. Furthermore, the protocol was applicable to the synthesis of tetrahydro-β-carbolinones and was effective for cyclization of unprotected indoles. 2-(3-Butenyl)indoles underwent platinum-catalyzed cyclization with exclusive 6-endo-trig regioselectivity. Mechanistic studies established a mechanism for the platinum-catalyzed cyclization of 2-alkenyl indoles involving nucleophilic attack of the indole on a platinum-complexed olefin.

Catalytic intramolecular crossed aldehyde--ketone benzoin reactions: a novel synthesis of functionalized preanthraquinones.

Abstract: Stereochemically and functionally rich polycyclic compounds are obtained by the first crossed aldehyde-ketone benzoin reaction in excellent yield under mild reaction conditions (5-20 mol % thiazolium salt, 10-70 mol % DBU, tBuOH, 40 degrees C, 30 min). This novel catalytic methodology offers a convenient approach to sophisticated molecular architectures useful for the stereocontrolled construction of polycyclic compounds as well as the fully regiocontrolled synthesis of anthra- and naphthoquinones.

N-tosyloxycarbamates as reagents in rhodium-catalyzed C-H amination reactions.

Abstract: Metal nitrenes for use in C-H insertion reactions were obtained from N-tosyloxycarbamates in the presence of an inorganic base and a rhodium(II) dimer complex catalyst. The C-H amination reaction proceeds smoothly, and the potassium tosylate that forms as a byproduct is easily removed by filtration or an aqueous workup. This new methodology allows the amination of ethereal, benzylic, tertiary, secondary, and even primary C-H bonds. The intramolecular reaction provides an interesting route to various substituted oxazolidinones, whereas the intermolecular reaction gives trichloroethoxycarbonyl-protected amines that can be isolated with moderate to excellent yields and that cleave easily to produce the corresponding free amine. The development, scope, and limitations of the reactions are discussed herein. Isotopic effects and the electronic nature of the transition state are used to discuss the mechanism of the reaction.