7e-butyl

Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1010) 95 % aqueous ETOH 1178 1.7E-15 4.5 E-13... 

Dicyanomethylidene)-2,6-di-/ert.-butyl (or phenyl)-4//-tellurin was oxidized by per-oxyacetic acid and converted to the 7e,7e-diacetate by acetic acid in dichloromethane1. 

A complete removal of the conjugated Jt system, as in the cydohexyl analogue 7c, also resulted in a minor decrease in enantioselectivity (to 85% ee, entry 12) as compared to the phenyl analogue 6b (94% ee, entry 1). However, it is pertinent to note that this decrease was found to be more substantial when the less bulky catalyst 22 was employed (37% ee at rt and 59% ee at 20 °C) [12b], demonstrating the superiority of Sigamide (35). With the less sterically hindered isopropyl derivative 7d, the enantioselectivity dropped to 62% ee (entry 13). On the other hand, the sterically much more congested tert butyl derivative 7e reacted sluggishly and the enantioselectivity was found to further decrease (entry 14) [12h]. 

A -Methylnicotinamide (7a) is oxidized predominantly at position 6 by rabbit liver aldehyde oxidase [60, 196, 197], As the size of the alkyl substituent increases (7b-7d), oxidation at carbon 4 becomes more favourable, and with the r-butyl analogue (7e) only 4-pyridone is produced (Table 3.7) [60, 197]. The Km for compounds (7a-7e) decreases with increasing size of the alkyl group, pointing to a higher affinity for those compounds with more hydrophobic substituents. However, the larger branched alkyl groups not only sterically hinder oxidation at carbon 6 but also decrease the overall oxidation rate. The major products of aryl or arylalkyl-substituted 3-carbamoylpyridinium chlorides (7f-7n) with rabbit liver aldehyde are also 6-pyridones [51]. 

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