Tetramethylpiperidine-1 -oxyl-4-amine

M. x 108M 1s 1 at 25°C, but may be appreciably lower in the solid state. In comparison k2 for oxygen competition for the alkyl radical is 2 x 109M-1s 1. Thus for air-saturated PPH ([02] 8 x 10-1,M)reaction7 will be protection against xenon irradiation was improved as compared to the parent piperidine by about 25, but the nitroxide itself was reduced to the 1 x 10 M level within the first lOOh and persisted at this level until brittle failure (7,) In contrast the parent amine is completely destroyed in the first lOOh of xenon exposure. 

TABLE 10.2 Addition Rate Constants kj of Various Radicals to Monomers Reaction Rate Constants kr of These Radicals with Oxygen, an Amine, a Stabilizer (HQME Hydroquinone-Methyl Ether) and a Spin Trap (TEMPO 2,2,6,6 Tetramethylpiperidine N-Oxyl). 

At this juncture, the stereochemistry of the amine-substituted carbon required inversion to the correct configuration of the natural product. Toward this end, lactone 354 was treated with tetramethylguanidine and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) under an air atmosphere in THE. These conditions led to oxidation to yield enamine 355, which was subsequendy reduced with sodium cyanoborohydride to complete the epimerization process. These conditions were also sufficiently hydridic to reduce the ketone carbonyl. Heating in ethyl acetate then led to cycHza-tion to yield lactam 356. Oxidation using IBX next provided ketone 357, which was employed as a coupling partner for 2-iodoanihne in the key indolization step (Scheme 51). 

The electrochemical behavior of tris(4-bromophenyl)amine (xxiii) and 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO, xxiv) was comparatively studied in [C4mim][CF3S03], [C4mim][BF4], and [C4mim][PF6] [18]. TEMPO showed a... 

Oxidation of 50 (Scheme 10.8) with 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and bis[acetoxy(iodo)]benzene (BAIB) in a 1 1 mixture of acetonitrile and water [66], afforded acid 47 in good yields. The two amines 45 and 46 were synthesized from 49 and 50, respectively, via the corresponding azides (Scheme 10.8). Functionalization of44-47 with the m-alkyne linkers (Scheme 10.10) yielded the 11 linker-armed Gal fragments 54-64 used in the library. 

Where more selective oxidations are required, oxidants such as (2,2,6,6-tetramethylpiperidin-l-yl)oxyl (free radical) (TEMPO) 12 have been successfully employed, as illustrated in Scheme 6.7, for the bleach 13 oxidation of alcohols to aldehydes.Other homogeneous oxidants employed under flow conditions include oxone and iron nitrate, " with Koch et al. using the periodic acid/H2S04 mediated oxidative deprotection of / -methoxyphenyl protected amines. 

For grafting, the amines were purchased from Aldrich Chemical Co 4-amino 2,2,6,6-tetramethylpiperidine-l-oxyl radical (called 4-amino TEMPO), n-octylamine, /j-butylamine and 2-methoxyethylamine (Table 2). 

---