Silver carbonate diols

Silver carbonate, alone or on CeHte, has been used as a catalyst for the oxidation of methyl esters of D-fmctose (63), ethylene (64), propylene (65), trioses (66), and a-diols (67). The mechanism of the catalysis of alcohol oxidation by silver carbonate on CeHte has been studied (68). 

Concomitant protection of the amino group and the cis-hydroxyl group of the diol 342 was realized by treatment with formaldehyde to afford the oxazolidine 345, oxidation of which with silver carbonate on Celite gave the... 

Optimum yields of (3-vinyl-y-butyrolactols from the Pd(II) promoted reaction of vinyl triflates with Z-but-2-en-l,4-diol (Scheme 6.33) are attained when tetra-n-butylammonium chloride is added (47]. The lactol is conveniently oxidized to the lactone with celite-supported silver carbonate. The corresponding arylbutyrolactols are obtained in high yield (70-80%) from an analogous reaction of iodoarenes with the enediol. The yields of 2-alkenyl-2,5-dihydrofurans, resulting from the Pd(0) catalysed reaction of cyclic alkynylcarbonates with acrylic esters via tandem C-C and C-0 bond forming reactions, are enhanced by the presence of tetra-n-butyl-ammonium fluoride (e.g. Scheme 6.33) (48]. 

A corollary of this selectivity is the very easy transformation of diols into lactones with silver carbonate on Celite .16 During the oxidation of a diol with Fetizon s reagent, as soon as an intermediate hydroxyaldehyde is able to equilibrate with a certain proportion of hemiacetal—even if present... 

For the synthesis of the tetrasaccharide unit (267) of the blood-group substance A (type 1), Paulsen and Kolar [192, 193] prepared the benzoate (269) by partial benzoyl-ation of the diol (268) and condensed this with 2,3,4-tri-O-benzyl-a-L-fucosyl bromide in the presence of tetraethylammonium bromide to give (270) in 82% yield. The benzoyl group was removed to give (271) and this was condensed with the chloride (274) in the presence of silver carbonate — silver perchlorate to give the tetrasaccha-... 

M. Fetizon, M. Golfier, and J. M. Louis, Highly selective oxidations of diols by silver carbonate, Chem. Commun., (1969) 1102 A new synthesis of lactones application to ( )-mevalonolactone, ibid., (1969) 1118-1119. 

Oxidation.—Silver carbonate on celite (Fetizon s reagent) reacts non-selectively with a pregnane-18,20-diol (60), giving the lactone (6l) and the lactol (62).82 Special conditions have been described for the selective oxidation of 5a -androstane-3/3,6/3-diol with Fetizon s reagent to give the 3-oxo-derivative as major product. The 3/8,6a-diol readily gives the 3-oxo-derivative in good yield.83... 

The selective oxidation of diols in which one or both hydroxy groups are allylic has been reported on a number of occasions. Reagents which have proved use for this include silver carbonate on Celite, barium manganate/ and manganese dioxide, as illustrated in equations (29)-(31). 

Silver carbonate on Celite itself is a highly selective reagent for this type of chemoselective oxidation as can be seen from the examples in Scheme 17 secondary diols can be oxidized to the hydroxy ketones, and primary diols are oxidized to lactones (see Section 2.9.2.2). 

Historically, the first supported oxidizing reagent, reported by Fdtizon and Golfier, was silver carbonate on celite (another diatomaceous earth). This was obtained by precipitation of the reagent onto its support. Ag2C03 on celite smoothly oxidizes primary and secondary alcohols, a,(o-diols, hydroquinones and amines. The main practical asset of the reagent is that it avoids the need to filter off finely divided silver salts after reaction. 

Ag2C03/Celite (Fetizon s reagent) (silver carbonate on Celite) Hexane benzene chloroform RT, Reflux 2 alcohol—) ketone diols—) lactones... 

Oxidation of the primary alcoholic group to a carboxyl group in diols with primary and secondary hydroxyls is accomplished by silver carbonate [377]. Unfortunately, an extremely large excess of the reagent is needed. Similar results are obtained with a rather exotic oxidant, 4-methoxy-2,2,6,6-tetramethyl-l-oxopiperidinium chloride, which is prepared by treatment with chlorine of a stable radical, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl. The compound oxidizes 1,4-butanediol to y-butyrolactone in 100% yield (isolated yield 81%) and 1,5-pentanediol to 8-valerolactone in 61% yield (isolated yield 40%) [995] (equation 292). 

Diols with primary and tertiary hydroxyls also give lactones on treatment with silver carbonate, but diols with primary and secondary hydroxyls yield, besides lactones, hydroxy ketones, resulting from preferential oxidation at the secondary center (equation 293) [377]. 

In another synthesis the diol 155 was oxidized with silver carbonate on Celite to the lactone 156 convertible (lithium dimethyl cuprate, debenzylation, and dehydration) to ( )-eldanolide [( )-129]. Finally a synthesis of racemic eldanolide involved coupling of a C4 unit, 157, with 4-methyl-3-pentenal. In tetrahydrofuran at -78 C, the reaction occurred at the y-position to the metal atom (158) to yield 72% of the alcohol 159, which gave 98% ( )-129 with mercuric chloride. ... 

The oxidation of a-, j8-, and -y-disecondary diols leads to hydroxy ketones, unless forcing conditions are used (large excess silver carbonate, many hours reflux) 1,7- and 1,8-diols also give hydroxy ketones.2 Examples ... 

Lactones. Primary 1,4-, 1,5-, and 1,6-diols are oxidized to lactones in satisfactory yield by silver carbonate on Celite (20-25 eq.) in refluxing benzene (1-30 hr.f... 

It is possible to run a controlled over-oxidation reaction with silver carbonate. Fetizon discovered that 1,3-and 1,4-diols are smoothly oxidized to butyrolactone and valerolactone derivatives in good yield. Oxidation of a diol can be accomplished in the presence of a variety of functional groups, even another alcohol. A primary alcohol, for example, will be oxidized faster than a secondary alcohol, as illustrated by the conversion of 113 to 114.173... 

---