Oxidation lead tetraacetate, oxidative cyclization

Lead tetraacetate oxidation was applied to construct a benzo[c]-phenanthridine skeleton. The Hofmann degradation product 224 derived from the phenolic protoberberine 59a was oxidized with lead tetraacetate to afford the p-quinol acetate 225, which was cyclized to the benzo[c]-... 

Unexpected formation of the oxoadamantane skeleton is observed during a series of transformations of the alkaloid lycopoline 153 lead tetraacetate oxidation of the alcohol (131) gives a 90% yield of the oxaadamantane (132), which is opened to 133 with boron trifluoride in acetic anhydride and re-cyclized to 132 with aqueous hydrogen bromide. 

Oxidative cyclization of acylhydrazones 110a, derived from aldehydes or ketones, with the use of lead tetraacetate (LTA) has been developed into a useful route to several disubstituted and tetrasubstituted oxadiazole derivatives 122, being a convenient source of relatively stable carbenes, like N(0)C , S(0)C , 0(0)C , or S(S)C <2000J(P1)2161 >. Some representative recent examples of the syntheses are collected in Table 2. 

Thus, the substituted tetrazoles 113 upon oxidation with lead tetraacetate gave rise to the fused tetrazoles 114, in most cases in high yields. Tetrazole derivatives 115, bearing an anisidine side chain, also underwent oxidative cyclization and afforded 10-methoxycarbonylmethyltetrazolo[l,5- ]quinoxaline 116 in good yield. This compound was obtained as a mixture of tautomers (with participation of the methylene hydrogen atoms) and the depicted tautomeric form 116 proved to be dominant. 

Diethyl N-(4-Aminophenyl)aminomethylenemalonate (167, R = H) was reacted with N, Af -bis(methoxycarbonyl)-5-methylisothiourea in the presence of p-toluenesulfonic acid in boiling methanol for 4 hr to afford the guanidine derivative (1590) in 50% yield. The guanidine (1590) was oxidized in chloroform with lead tetraacetate to the quinoline diimine (1591), which cyclized to 1592. After methanolysis, the 2-(methoxycarbon-ylamino)benzimidazole derivative (1593) was obtained in 41% yield [86JCR(S)161]. 

Oxandrolone Oxandrolone, 17j3-hydroxy-17a-methyl-2-oxa-5-androstan-3-one (29.3.10), is made by oxidation of the C1-C2 double bond of 17j3-hydroxy-17a-methyl-l-androsten-3-one by a mixture of lead tetraacetate and osmium tetroxide with an opening of the A ring of the steroid system, which forms an aldehyde acid (29.3.9). Upon reducing the aldehyde group with sodium borohydride, intramolecular cyclization takes place, directly forming a lactone (29.3.10), which is the desired oxandrolone [31,32]. 

Synthesis of alkaloids enamide cyclizations for, 22, 189 (1983) lead tetraacetate oxidation in, 36, 70 (1989)... 

SCHEME 40. Hale, Hough, and Richardson s studies on the reductive animation (1988) and Fischer cyclization (1987) of a 3, 4 -dialdehyde derived from lead tetraacetate oxidation of sucrose. The glycosyl morpholines were very sweet ... 

The mixed hydrazones (667), prepared from diacetyl monobenzoyl hydrazone and arylhydrazines, undergo oxidative cyclization to 2-aryl-jV-benzoyl-4,5-dimethyl-l,2,3-triazol-l-ylimines (668) in 32-76% yield upon treatment with lead tetraacetate in acetonitrile (Scheme 132) <92JOC2252>. The cychzation of bishydrazones to 1,2,3-triazoles can also occur in acidic or basic media. For instance, the tetrahydrobenzo[ /]triazol-4-one (669) is prepared by the base-catalyzed cyclization of the corresponding a-hydrazono oxime (Equation (53)) <85HCA1748>. 3-Methyl-1,2-cyclohexanedione reacts... 

Lead tetraacetate oxidative cyclization of the A-(l-naphthylvinyl)urethane 30, derived from I -acetonaphthone 28, yields 4-naphthyl-2(3//)-oxazolone 32 as the... 

Oxidation of the 1-aminoquinazolinones (44) with lead tetraacetate culminated in the intramolecular addition of the resulting N-nitrene intermediate to the triple bond to give the pyrrolo[2, l-b]quinazoline (45) [85CC544 86JCS(P1)1215]. The pyrrole ring of 47 was also formed by cyclization of 2-methyl-3-phenacylquinazolin-4-one (46) with dilute aqueous alkali followed by fusion (86T4481). 

Two closely related mesoionic systems, 59 and 60, were obtained by reductive cyclization of 61 with TEP,62 and by oxidation of 62 with lead tetraacetate,63 respectively. The pyrazolo[4,3-c]pyrazole 64 was obtained from the azo compound 63 by reduction with dithionite, followed by diazotization of the resultant amine and cyclization with... 

Oxidation of 2-azidophenyl ketone hydrazones (455) affords the 2-azidophenyldiazoalkanes (456) which can be cyclized thermally to 1,2,3-benzotriazines (457) (75JCS(Pl)3l). Similarly, 2-aminophenyl ketone hydrazones (458) give 1,2,3-benzotriazines (457) on oxidation with lead tetraacetate (75JCS(Pl)3l). 

Aryl-l, 2,4-triazolo[l, 5-a]pyrimidines (17) were prepared by oxidative cyclization, by the action of lead tetraacetate (LTA), of 2-pyrimidylary-lamidines (16), first prepared by the reaction of 2-aminopyrimidines (15) with aryl cyanides in the presence of A1C13 (90SC2617) (Scheme 6). 

The unsubstituted 2-benzopyrylium cation 1 was first synthesized by Blount and Robinson (33JCS555) starting with indene. Its oxidation by lead tetraacetate affords homophthalic dialdehyde, which is cyclized to 2-benzopyrylium tetrachloroferrate on treatment with hydrochloric acid and ferric chloride. 

The derivative (22) has been prepared in two ways (Scheme 4). The diazo compound (59), made by diazotization of the 3,4,5-triamino-l,2,6-thiadiazine 1,1-dioxide (61), cyclizes upon heating in water to give the bicyclic heterocycle (22) in 80% yield. Alternatively, the same product (22) has been obtained by treatment of the 3,5-diamino derivative (60) with tosylazide. With phenyl-diazonium chloride, the diamine (60) gives the diazo compound (63) which, upon oxidation with lead tetraacetate, gives the 2-phenyl derivative (62). Attempts to oxidize the corresponding m-Cl and p-N02 phenyl compounds failed <77JHC427,77MI714-01). 

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