Azides ethanesulfonyl

A further use of Barton esters has been described as a path to enol ether radicals. The reaction involves the photochemical decomposition at 355 nm of the derivative (85). As part of an approach to the synthesis of a series of Kopsia alkaloids, the reductive decarboxylation of the derivative (86) was carried out. This involved irradiation of the Barton ester (86a) in the presence of t-BuSH. This affords the product (86b). The photochemical decomposition of the Barton ester (87) provides a path to the silyl derivatives (88). The nature of the trapping agent X is dependent on the conditions under which the reaction is carried out. Thus a variety of derivatives can be obtained using alcohols to afford ethers, or using ethanesulfonyl azide to give azides. The Barton esters (89) undergo the usual photochemical decarboxylation to afford ethenoyloxy radicals. Cyclization within these, in the presence of tributylstannane yields the lactones (90). ... 

The only example of the 1,4,5-benzoxathiazepine system (173) has been obtained from 2-(aryloxy) ethanesulfonyl azides (171) either by thermal decomposition in oxygen-free Freon 113 or by flash vacuum pyrolysis via the adducts (172) derived from the initially formed ethanesulfonylnitrenes (Scheme 27) <84JOC3ll4>. 

The hydrohydrazination represented a general solution for the amination of alkenes, but the protected hydrazines obtained are sometimes difficult to transform to the free amines. At this point, we turned to sulfonyl azides as nitrogen sources, based on then-capacity to react both with enolates and carbon-centered radicals. Mechanistic investigations of the hydrohydrazination reaction had suggested a radical character for the formed organocobalt intermediate. " We were pleased to see that the Cobalt-catalyst 4 was able to promote the hydroazidation of 4-phenylbut-l-ene (3) with ethanesulfonyl azide (7), giving the product derived from the formal Markovnikov addition of hydrazoic acid onto the C-C double bond exclusively, albeit in moderate yields (50%). 

We then examined complexes 11a and 11b derived from a,a-diphenylglycine. Complex 11b displayed increased reactivity when compared to standard catalyst 4, and azide 8 was obtained in 8 h in 70% yield with ethanesulfonyl azide (7) from 4-phenylbut-l-ene (3). Catalyst 11b could be synthesized from the corresponding ligand 12 and Co(II) salts under oxidative conditions (Scheme 4.2). Ligand 12 was easily available from 3,5-di-tert-butylsalicylaldehyde (13) and a,a-diphenylglycine (14). Recently, ligand 12 has also become commercially available from Aldrich under the name SALDIPAC. ... 

The structural features of 11b are noteworthy even in the presence of excess amino acid, only the 1 1 complex of 12 and Co was detected by NMR spectroscopy in sharp contrast to complex 4 (Fignre 4.4). This is probably due to the steric bulk of ligand 12 and explains its increased reactivity and lower stability. Unfortunately, we were unable to obtain reproducible results using complex 11b, as yields (40-70%) and reaction time (8 8 h) were batch-dependent. In many cases, an initiation time was observed before the reaction started. Mukaiyama and co-workers used ferf-butyl hydroperoxide as a cobalt-catalyst for the hydration of certain olefins when initiation of the reaction was difficult. A similar effect was observed in the hydroazidation reaction when using catalyst 11 with ethanesulfonyl azide (7) for the hydroazidation of 4-phenylbut-l-ene (3), complete conversion was observed after 2-8 h using 30% of ferf-butyl hydroperoxide. In situ formation of complex 11b in the reaction mixture leads to reproducible reaction times (2h) and yields (70%). Co(BF4)2-6H20 was the best Co salt for this procedure, as complex formation was faster than with other salts and quick oxidation to the Co(III) complex occurred in the presence of tert-butyl hydroperoxide. 

Finally, we examined the effect of varying the silane structure on reaction rate and selectivity. The use of tetramethyldisiloxane (TMDSO) (entry 5) showed a small but significant increase in the azide/alkane ratio (84 16 vs. 77 23 with ethanesulfonyl azide (7)). The reaction with poly(methylhydrosiloxane) (PMHS) was too slow (entry 6). However, addition of a sub-stoichiometric amount of phenylsilane was enough to give useful conversion (entry 7). Triethylsilane and triethoxysilane (entry 8 and 9) could not be used. Finally, combining tosyl azide (17) and TMDSO gave full conversion of 4-phenylbut-l-ene (3) in 3h with an improved azide/alkane ratio of 96 4 (entry 10) and 86% isolated yield. 

In order to broaden the scope of the reaction, ethanesulfonyl azide was replaced by benzenesulfonyl azide and in the presence of hexabutylditin as chain transfer reagent. Because of the instability of the phenyl radical, the intermediate benzenesnlfonyl radical does not liberate SO2. The proposed chain reaction is described in Scheme 8.27. Under these reaction conditions, the azidation reaction is clean and fast (<4h) and purification of the products is easier than in the procedure involving EtSOsNs. Cyclization reactions are efficiently performed (Scheme 8.27). 

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