Intramolecular with sulfamate esters

Generally, hydrocarbons tethered with sulfamate esters or carbamates are suitable substrates and afford five- or six-membered ring products through intramolecular C-H amidation. For reasons not yet understood, carbamates and sulfamate esters prefer to form five- and six-membered rings, respectively. In general, this important and useful selectivity can avoid formation of product mixtures, a major drawback for similar organic transformations. 

With the iron complex [Fe(Cl3terpy)2]( 104)2 (Clsterpy = 4,4, 4"-trichloro-2,2 6, 2"-terpyridine) as catalyst, sulfamate esters react with Phl(OAc)2 to generate iminoiodanes in situ which subsequently undergo intramolecular nitrenoid C-H insertion to give amidation products in good yields (Scheme 30) [48]. 

The sulfamate ester variant of this chemistry has already been shown to be a very powerful protocol for the syntheses of 1,3-amino alcohols and related /3-amino acids (Equation (90)), as well as iminium ion equivalents (Equation (91)). The further showcases of this chemistry are the total syntheses of the bromopyrrole alkaloids, manzacidins A and C (Scheme 13).234 The cyclic sulfamidate 129 was obtained diastereospecifically from sulfamate 128 using intramolecular rhodium-catalyzed G-H insertion. It was then found to react with sodium azide in NfN-dimethylformamide at room temperature after introduction of the Boc-activating group to afford the 1,3-diamino precursor 130 in 78% yield over 3 steps. Four subsequent manipulations afford the target structure 131. 

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

After successful application of the silver catalyst shown in olefin aziridination (Section 6.1.1), He and coworkers showed that intramolecular amidation was possible with both hydrocarbon-tethered carbamates and sulfamate esters.24 They found that only the Bu3tpy silver complex could catalyze efficient intramolecular amidation, while other pyridine ligands gave either dramatically lower yields or complicated product mixtures. In an interesting control study, both copper and gold were also tested in this reaction. Both the copper and gold Bu tpy complexes can mediate olefin aziridination, but only silver can catalyze intramolecular C-H amidation, indicating that the silver catalyst forms a more reactive metal nitrene intermediate. 

In addition to epoxides, three-membered nitrogen heterocycles, aziridines, can be obtained by means of catalytic asymmetric aziridinations (Eq. 30). To this aim, chiral ruthenium(salen) complexes 67 [56] and 68 [57] were useful (Fig. 1). The former phosphine complexes 67 gave the aziridine from two cy-cloalkenes with 19-83% ee [56]. On the other hand, terminal alkenes selectively underwent aziridination in the presence of the latter carbonyl complex 68 with 87-95% ee [57]. In these examples, N-tosyliminophenyliodinane or N-tosyl azide were used as nitrene sources. Quite recently, catalytic intramolecular ami-dation of saturated C-H bonds was achieved by the use of a ruthenium(por-phyrin) complex (Eq. 31) [58]. In the presence of the ruthenium catalyst and 2 equiv iodosobenzene diacetate, sulfamate esters 69 were converted into cyclic sulfamidates 70 in moderate-to-good yields. 

Both N-N and N-C bond fission occurs on irradiation of the hydrazone derivatives (191). The photodegradation of the phenylhydrazone and the hydrazone of benzil have also been described. a-Ketoiminyl radicals are formed on irradiation of oximino ketones at low temperature. A study of the photochemical decomposition of sulfamic esters and their use as initiators of cross-linking of a melamine resin have been described. The bispyridinyl radical (192) is formed by one electron reduction of the corresponding pyridinium salts. The irradiation of this biradical at 77 K results in C-N bond fission with the formation of benzene-1,3-diyl. The predominant products from the irradiation (X,> 340 nm) of (193) in methanol were identified as A -hydroxy-2-pyridone and (194) from the fission of the C-O bond. Other products were 2-pyridone, (195) and (196) that arise from O-N bond fission. The reaction is to some extent substituent dependent and a detailed analysis of the reaction systems has identified an intramolecular exciplex as the key intermediate in the C-O bond heterolysis. 

A recent DFT study has shown that retention of configuration observed for the above reactions is in agreement with the insertion of singlet nitrene and a concerted product formation [150 is the transition state for the reaction shown in Equation (6.135)]. Du Bois and coworkers have performed detailed mechanistic investigations of the intramolecular sulfamate ester C-H amination reaction catalyzed by a dirhodium complex. Reactivity patterns, Hammett analysis, and kinetic isotope effect studies have provided support for the concerted, asynchronous transition structure 151. A similar conclusion was arrived at for an analogous intermolecular process. ... 

A highly effective Ru-eatalyzed asymmetric intramolecular amination of benzylic and allylic C—H bonds was developed in 2008 by Blakey and coworkers. Ru-Pybox complexes were readily prepared by using Nishiyama s method. Initially, the reaction was tested without any additives. However, the desired product 133 could be produced in only modest yields and ee values (Table 1.10, entries 1-3). Based on the studies by Du Bois, the authors rationalized that a cationic catalyst would be more reactive than the neutral one. Thus, the catalyst prepared from halide abstraction by AgOTf gave improved yields and selectivities (Table 1.10, entries 4-6). Further screening of ligands, solvents, and temperature led to the optimal conditions reaction of sulfamate ester 132 with 5 mol% of C16,110 mol% of PhI(OAc)2, and 230 mol% of MgO in benzene at 4 °C (Table 1.10, entries 7-14). Under these conditions, a series of five- and six-membered-ring products were obtained with up to 71% yield and 92% ee. Notably, the cis-olefin substrate 135 could also participate in the reaction (Scheme 1.50). Under the standard conditions, the... 

Wehn et ah have also reported the intramolecular aziridination of chiral homoallyl sulfamate esters, sueh as 216, with moderate selectivity. The bicyelie... 

Terpyridine ligands were also incorporated to an iron catalyst system [34], In 2008, Che and coworkers developed a highly effective iron(II) catalyst with 4,4, 4"-trichloro-2,2 6, 2"-terpyridine (Claterpy) 17 for aziridination of alkenes with the iminoiodinanes (Scheme 2.21), and intramolecular amidation reactions of sulfamate esters [35]. 

Sulfamate indan-2-yl ester 145 is oxidized by iodobenzene diacetate to give condensed 1,2,3-oxathiazole di-A-oxides 146 (Equation 35). Various rhodium <2001JA6935, 2004HCA1607>, manganese(m) Schiff base <2005TL5403>, and ruthenium porphyrin <2002AGE3465> catalysts can be used for this transformation. Enantioselective intramolecular amidation is achieved with good yields. 

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