Deoxygenated reaction time

Figure 1. Effect of gamma irradiation on the oxygencarrying capacity of different concentrations of oxygenated hemocyanins in phosphate buffer at pH 7.0. The oxygenation reaction time was 10 minutes and the deoxygenation reaction time was 30 minutes...

The duration of these reactions appears to be extremely important as longer reaction times resulted in deoxygenation of the thiophene derivative. 

Rhodium-catalyzed hydroformylation of -(substituted amino)benzyl-amines (387, X = H2) and -(substituted amino)benzamides (387, R = H, X = O) in the presence of rhodium(II) acetate dimer and triphenylphos-phine in deoxygenated ethyl acetate gave a 7 3 mixture of 1,2,3,4,4 ,5-hexahydro-6//-pyrido[l,2-a]quinazolines (388, X = H2,0) and isomeric 3-methyl-l,2,3,3fl,4,5-hexahydropyrrolo[l,2-a]quinazolines (389, X = H2, O) (94AJC1061). The methyl derivative of benzylamine 387 (R = Me, X = H2) afforded a mixture of diastereoisomers 390 and 391 (X = H2). Their ratio depended on the reaction time. Longer reaction times gave more 391 (X = H2), containing the methyl group in an equatorial position. Compound 390 isomerized into 391 (X = H2), under the aforementioned conditions. The benzamide derivative (387, R = Me, X = O) yielded only one isomer (391, X = O), independent of the reaction period. 

Quinoxaline 1,4-dioxide undergoes reaction with acetyl chloride and substitution occurs in the benzene ring to give 6-chloroquinoxaline 1 -oxide and, on increasing the reaction time, 3-chloroquinoxaline 1-oxide and 6,7-dichloroquinoxaline appear as additional products.A similar reaction is observed with 3-phenylquinoxalin-2(l//)-one 4-oxide and its 7-substituted derivatives, where ring substitution at position 6 again is accompanied by deoxygenation. 2-Chloroquinoxalinc 1-oxide (19) is obtained in 60% yield by treatment of quinoxaline 1,4-dioxide with benzenesulfony chloride and consequent neutralization of the benzenesulfonate initially formed,and in addition about 3% of 3-chloroquinoxaline 1-oxide is formed. 

The Chapter on Photochemical, Radical, and Deoxygenation Reactions does not appear this year because of illness of the Reporter at a critical time. 

The conversion never reaches 100% whatever the reaction time, suggesting deactivation of the catalyst. Indeed, after addition of the epoxide, the intensity of signal B decreases with time. Similarly, the initial red-orange colour fades with time and vanishes at the end of substrate conversion. This colour may be attributed to the active complex. The catalytic site proposed above involves an oxophilic Ni centre. Deactivation might arise from oxidation of this active complex and simultaneous epoxide deoxygenation yielding the small amount of allylic tertiary alcohol la observed (Table 3). 

A freshly-prepared, pale yellow, soln. of AII3 in dry benzene added with stirring to a soln. of 5,6a-oxido-5a-cholestane in acetonitrile, and reaction continued for 5 min - cholest-5-ene. Y 95%. Longer reaction times were required for less reactive epoxides which initially afforded rra/i5-1,2-iodohydrins. F.e. and preferential deoxygenation s. P. Sarmah, N.C. Barua, Tetrahedron Letters 29, 5815-6 (1988). 

Deoxygenation and Desulfurization. Hexachlorodisilane has been shown to effect the stereospecific reduction of phosphine oxides to phosphines with inversion of configuration (eq 1 ), although short reaction times are required to prevent chemical racemization of the phosphine products under the reaction conditions. This protocol complements trichlorosilane which, under appropriate conditions, reduces phosphine oxides with retention of configuration. Reductions of bridged bicyclic phosphine oxides and cyclic halophospholene oxides by hexachlorodisilane have also been reported. 

At the same time, the reaction of 1,2,4-triazine 4-oxides 55 with the anion of chloromethyl phenyl sulfone affords 5-(l-chloro-l-phenylmethyl)-l,2,4-triazines 66. In this case, autoaromatization of the a -adducts proceeds by the deoxygenative... 

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