Deoxygenative process

Nitrification as a deoxygenation process is normally significant only in river systems receiving pollutional inputs of ammonia. The kinetics of nitrification are less clear than those for carbonaceous deoxygenation (33). 

A fused OZT was obtained in the course of the reduction of vicinal azido-thiocarbonates via formation of the intermediate amine, which attacks the thiocarbonyl group (Scheme 37). The condensation reaction proved faster than the deoxygenation process for the synthesis of 2 -amino-2, 3 -dideoxyuridine50 or methyl 3-amino-4,6-0-benzylidene-3-deoxy-2-0-phenoxythiocarbonyl-a-L-talopyranoside.51... 

Most electrophilic carbenes, such as 2/f-imidazolylidenes and 3H- and 4i/-triazolylidenes, in nitrobenzene gave rise to deoxygenation processes involving the intermediacy of the ylide 42, which decomposed to ni-trosobenzene and 43 (Scheme 12). However, the azolones 43 are too unstable to be detected or trapped in the reaction conditions. 

The triethyl phosphite deoxygenation process tolerates aromatic bromine, methoxyl, ° ° ° phenyl, and in-... 

Carbonylcarbene reacts with oxetane in a complex manner, giving cyclopropane and propene by a deoxygenation process and ketene plus ethylene as apparent insertion-fragmentation products (equation 66). The reaction is carried out by irradiation of a solution of carbon suboxide in oxetane under these conditions, photodecomposition of intermediates is possible. The initial attack is believed to be at the ring oxygen atom to give a zwitterionic species (78JA6425). 

C KIEs experiments were supposed to help distinguishing the rate-limiting formation of an epoxide-carbene ylide complex 52 versus a rate-limiting deoxygenation process. 

Sml2 has also been employed as a stoichiometric reductant in deoxygenation processes catalysed by palladium complexes.69 For example, allylic acetates can be reduced by treatment with Sml2 and 2-propanol in the presence of a palladium ) catalyst. Unfortunately, this reduction often generates regioisomeric and stereoisomeric mixtures of alkenes (Scheme 4.54).69... 

In fact, only in some cases are real carbenoid species involved in these reactions. The reactions employing oxophilic metals such as Zn, Fe, Sm, and In were reported [9], and representative examples are given in Scheme 3. Such reactions exhibit obvious synthetic limitations, since only aromatic (unsaturated) carbonyl compounds can be used, and/or cyclopropanes of a very specific structure obtained. The Kulinkovich and related reactions, involving dianion equivalents (1, Scheme 1), represent the only synthetically useful deoxygenative process at present. 

Owing to its physiological importance the oxygenation-deoxygenation process in hemoglobin has been widely investigated, but it is beyond the purposes of the present paper to give an account of the studies so far reported (see e.g. Ref. 127 for recent reviews), except for some main aspects. 

Methods of deoxygenation of nitrones (28), nitrile oxides (29), heteroaromatic N-oxides (30) and tertiary amine oxides (31) are described in this section. There are some reagents, such as trialkyl phosphites, which can deoxygenate compounds of all these types as well as those in the preceding section, whereas others are more limited in scope. Oae and coworkers have outlined three distinct mechanistic types of deoxygenation process, which are illustrated in Scheme 17. Clearly, a mechanism of type C will not apply to tertiary amine oxides (31) on the other hand, these compounds are more easily deoxygenated than heteroaromatic N-oxides, such as (30), by some reagents because the aromatic N-oxides are inherently more stable. 

Table 3B lists the ten amino acid residues in the o chain and the nine amino acid residues in the /3 chain which form the area of lesser contact between unlike chains, the contact. As pointed out before, this contact undergoes the greatest shift during the oxygenation and deoxygenation process. 

Lloyd-Jones and co-workers discovered the direct synthesis of homoallyl-substi-tuted vinylcyclopropanes from w./Lunsaturated ketones and allylindium reagents. In this transformation, the indium-mediated deoxygenation process delivers two allyl units to a, -unsaturated ketones (Scheme 8.23) [40],... 

In the runs at 420°C and LHSV=1.6 h the yield of the liquid products was as high as 92% and the content of butadione in the latter attained 60% mol. Unfortunately, further elevation of the temperature resulted in the increase of deoxygenating processes formation of hydrocarbons becomes perceptible and the selectivity decreases. 

The slow step in the deoxygenation process is the collapse of the radical adduct 2. Under certain circumstances, this intermediate may be intercepted by the stannane, causing the formation of unwanted side-products arising mostly from further reactions of the thioformate 5 [2, 10). The various possibilities are depicted in Scheme 4, which also includes an example of formation of a methyl ether as a co-product in the reaction of a xanthate with tributylstannane [10b]. The yield is variable, depending strongly on the exact reaction conditions. 

Application of the deoxygenation process to ff-hydroxysulfides or P-hydroxysulfones results in the clean formation of ra j-olefins through ji-elimination of a thiyl or sulfonyl radical [17]. This mild, radical version of the Julia olefin synthesis, initially described by Lythgoe and Waterhouse [17a], has been applied by two groups in the total synthesis of (+)-pseudomonic acid C. The transformation shown in Scheme 9 is taken from the synthesis by Williams and coworkers [17b]. 

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