Rearrangement lactone-amide

Thallium(iii) acetate with (130) gives the rearranged lactone (131), whose structure was established by AT-ray analysis lead tetra-acetate reacts in an analogous manner. The endo-epimer of (130) gives similar rearranged lactones. Lactol (132) in aqueous alkaline solution gives (133) with chlorine, and further transformations of (133) are noted. Previous attempts to prepare (134) by treatment of (135) with base have given mainly (136). By use of dimethylform-amide as solvent, conversion of (135) into (134) proceeds efficiently. Full... 

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

As mentioned earlier in the discussion of cyclizations leading to (3-lactones, the (3-lactones formed from halolactonization of 1,4-dihydrobenzoic acids readily rearrange to produce bridged ring y-lac-tones.19 In some cases, the substitution pattern favors formation of the y-lactone even under conditions of kinetic control (equation 23).20 Synthesis of a variety of y-lactones by iodolactonization of dihydroben-zoic acid derivatives has been reported recently by Hart (equation 24).91 Attempted iodolactonization of the acid in the case where R = H resulted primarily in an oxidative decarboxylation however, iodolactonization was effected using the amide derivative. 

The lithium amides 98, prepared from 4-hydroxy—lactone and imines, rearranges in the presence of lithium chloride at low temperature to form -lactams 99 (Scheme 52) with cholesterol absorption inhibition properties <1999JOC3714, CHEC-III(2.01.3.10.10)69>. 

In a stereocontrolled route to thromboxane B2, Corey and coworkers used the Eschenmoser rearrangement for the preparation of lactone (91 Scheme 14). The product of the 3,3-sigmatropic shift, amide (90), is directly iodolactonized, thus avoiding often troublesome amide hydrolysis conditions. Another application involving a carbohydrate derivative was demonstrated by Fraser-Reid and coworkers (Scheme 15). Reductive elimination of benzylidene (92), followed by in situ alkylation, Wittig reaction, DIBAL-H reduction and rearrangement, led to amide (94), which was transformed into the corresponding pyranoside diquinane by double radical cyclization. 

In order to construct the sterically congested C7a quaternary chiral center in the natural product anisatin, T.P. Loh and co-workers developed an efficient strategy by way of an Eschenmoser-Claisen rearrangement. The resulting amide was converted to an e-lactone (reported by A.S. Kende) in four steps, thereby completing a concise formal synthesis of (+)-8-deoxyanisatin. Other attempted [3,3]-sigmatropic rearrangements to construct C7a stereocenter resulted in re-aromatized products. 

The first asymmetric total synthesis of the hasubanan alkaloid (+)-cepharamine was completed by A.G. Schultz et al. In order to construct the c/s-fused A/-methylpyrrolidine ring, the advanced tetracyclic lactone was first converted to the primary carboxamide by treatment with sodium amide in liquid ammonia. Next the Hofmann rearrangement was induced with sodium hypobromite in methanol initially affording the isocyanate, which upon reacting with the free secondary alcohol intramolecularly gave the corresponding cyclic carbamate in excellent yield. 

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