Deoxygenated analogs

Benzofuroxan is a very pale yellow crystalline solid, of melting point 72°. Its dipole moment is given by Tappi as 5.29 D, and the moments of eight other benzofuroxans, their molar refractivities, and melting points, are also recorded.It is appreciably steam-volatile, but far less so than its deoxygenated analog benzofurazan. Melting points of benzofuroxans are listed by Kaufman and Picard, and in Section X of this article. 

The enthalpy of formation difference for the solid phenolic cyclic dipeptides, 3-(4-hydroxybenzyl)-2,5-piperazinedione (cycloglycyltyrosyl) and its deoxygenated analog, 3-benzyl-2,5-piperazinedione (cycloglycylphenylalanyl) is —166.9 1.8 kJ mol , much... 

As a first extension of the new overall enantioselective a-alkylation of 2-ke-toesters we developed an efficient asymmetric synthesis of 3-substituted cyclic hemiketals of (o-hydroxy-2-oxoesters [42]. As is depicted in scheme 15, the metalated SAMP-hydrazones were trapped with a number of O-benzyl- and O-silyl-protected co-hydroxy-l-iodoalkanes, which after hydrazone cleavage and deprotection afforded the cyclic hemiketals (de, ee > 98%), structurally modified deoxygenated analogs of ulosonic acids. To our knowledge only two methods have been reported for the synthesis of similar simple tetrahydropyran derivatives [43,44]. 

Scheme 15. Diastereo- and enantioselective synthesis of structurally modified deoxygenated analogs of ulosonic acids [42]...

Nitropyridazines are reduced catalytically either over platinum, Raney nickel or palladium-charcoal catalyst. When an N-oxide function is present, palladium-charcoal in neutral solution is used in order to obtain the corresponding amino N-oxide. On the other hand, when hydrogenation is carried out in aqueous or alcoholic hydrochloric acid and palladium-charcoal or Raney nickel are used for the reduction of the nitro group, deoxygenation of the N- oxide takes place simultaneously. Halonitropyridazines and their N- oxides are reduced, dehalogenated and deoxygenated to aminopyridazines or to aminopyridazine N- oxides under analogous conditions. 

Attack on oxiranes by trivalent phosphorus (64HC(19-l)43l) provides a method of deoxygenation to alkenes with inversion (c/. Section 5.05.3.4.3(hY)) and this makes possible the interconversion of (Z)- and (f)-alkenes (Scheme 58) (B-74MI50505). Silicon nucleophiles behave analogously (76JA1265, 76S199). 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

Similarly, cyclization of 2-o-nitrophenylpyridine A-oxide gave 211, deoxygenation preceding cyclization, though in this case a trace of 8-carboline was isolated. The cyclization of 4-o-nitrophenylpyridine (219) to jS-carbohne by heating with ferrous oxalate presents no such difficulties and is easily achieved, although 219 is not very readily available. By analogy, it should be possible to obtain a mixture of a- and y-carbohne from 3-o-nitrophenylpyridine (220 R = NO2). 

MeO), cyclic phosphonates (50). The formation of (50) is strong evidence for the involvement of carbenes (51). Diethyl alkylphospho-nites (52) deoxygenate aromatic aldehydes upon heating only small amounts of the a-ethoxybenzylphosphinate (53), which is analogous to products obtained from trialkyl phosphites and aromatic aldehydes, are formed. 

Analogous deoxygenations were carried out with antibiotics such as nargenicin,[42] fortimicin,[43] seldomycin,[44 erythromycin,[45H47] with baccatin (taxol group),[48] the triquinane hirsuten,[49] the tuberculosis inhibitor a-C-mannobioside,[49a] and the steroids alisol,[50] and progesterone.[51]... 

Epiberberine and berberine were stereoselectively converted to fumaritrine (421) and its analog via 8,14-cycloberbines 216). The cycloberbine 432, derived from epiberberine (431) in the established way, was treated with p-toluenesulfonic acid in methanol and then with methyl iodide to give stereoselectively the cis-fused indenobenzazepine 433 in excellent yield (Scheme 86). Deoxygenation of the hydroxyl group in 433 was accomplished by treatment with methanesulfonyl chloride and subsequent reduction with sodium borohydride in dimethoxyethane to give (+ )-fumaritrine (421) (216). 

An analog (56) of isomer 53 was prepared by a structure proving synthesis (Scheme 13). It was proved that the syn isomer (57) obtained after deoxygenation is transformed spontaneously to the anti form (58). Phosphine (58) was stabilized as the phosphine oxide (59) (Scheme 14) [55],... 

The deoxygenation of aryl 2-nitrophenyl sulphides with tervalent phosphorus compounds is analogous to that of the corresponding ethers except that in many cases the anticipated phosphoranes, e.g. (87), are thermally unstable.58 The extra stability of spirophosphoranes allows them to be isolated, e.g. (13), if cyclic phos-phonites are used in deoxygenation.8... 

Electron-withdrawing groups decrease the rate of the fluoro Pummerer reaction, which, in certain cases,7 allows a DAST-mediated deoxygenation to compete with the introduction of fluorine alpha to sulfur. The reaction is compatible with a number of functional groups and can readily be carried out with nucleosides. Robins and coworkers4 reported the synthesis of a 5 -fluoro-5 -S-phenyladenosine analog using antimony trichloride as catalyst at room temperature. It should be noted that a-fluoro sulfoxides provide a convenient entry to terminal fluoroalkenes.3 8 9 10... 

The trend of antibacterial activity of these kanamycin derivatives with N-1 AHB (amikacin analogs) is similar to amikacin regardless of the presence of 3 -deoxygenation (Table 4.10). The design of amikacin is, however, less effective against AAC(6 ). One interesting finding is the difference between 3, ... 

Recently, Hanessian has reported methods for direct modification of tobramycin. Tobramycin (or nebramycin) differs from kanamycin B only in its 3 -deoxygenation, which makes tobramycin immune from the modification catalyzed by APH(3 ). A library of tobramycin analogs bearing various functionalities at 0-5 was prepared (Scheme 4.23). In general, these tobramycin analogs were less active than tobramycin (Table 4.15). However, compounds 157 and 159 showed activity against P. aeruginosa (ATCC 27853) (MIC = 12.5 fig/mL). 

Hydride reduction of 345, followed by hydrogenolytic deoxygenation of the resulting hydroxylactam afforded staurosporinone (293) (766) (Scheme 5.225). The same sequence was applied to the synthesis of the 12-methyl analog of staurosporinone (766). 

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