Butyrolactones rearrangement

Further examples of the utility of the allylic sulfoxide-sulfenate interconversion in the construction of various biologically active natural products include intermediates such as the /Miydroxy-a-methylene-y-butyrolactones (e.g. 63)128 and tetrahydrochromanone derivative 64129. Interestingly, the facility and efficiency of this rearrangement has also attracted attention beyond the conventional boundaries of organic chemistry. Thus, a study on mechanism-based enzyme inactivation using an allyl sulfoxide-sulfenate rearrangement has also been published130 131. 

D-Mannitol (63) has been used for the synthesis of y-butyrolactones, making again use of a Claisen rearrangement as the key step (Scheme 10). The C2-symmetrical 1,4-diol 65, obtained from 63 via the alkene 64 [28], could be converted to 67 by applying the Eschenmoser-Claisen variant. Cyclization to 68 was readily achieved upon heating 67 in xylene, establishing two differ-... 

The strategy for the synthesis of y-butyrolactones by Claisen rearrangement of acylated 1,4-diols has been already discussed (Schemes 6-11). A stereodi-... 

In the past few years, new approaches for the enantioselective synthesis of / -benzyl-y-butyrolactones appeared in the literature. Some of these approaches involve the asymmetric hydrogenation of 2-benzyl-2-butenediols (j [34]), the radical mediated rearrangement of chiral cyclopropanes (r [35]), the transition metal catalyzed asymmetric Bayer-Villiger oxidation of cyclobutanones n [36]), or the enzymatic resolution of racemic succinates (g [37]). 

In addition, there are [5 -> 3 + 2] fragmentations leading to acyclic products that result from the original fragments by rearrangement. Examples are 5-phenyl-l,2,3,4-thiatriazole (50) and related compounds with three ring heteroatoms and an exocyclic double bond (51),THF (52), y-butyrolactone (53), y-thiobutyrolactone (54), pyrroles (8,61), pyrrolidine (55), furans (56, 58), pyrazole (62), and isoxazoles (11, 63,64). Most of these molecules are thermally rather stable and their decomposition requires drastic conditions. 

Asymmetric induction has been reported for a ketene Claisen rearrangement of the adducts of dichloroketene to chiral allyl thioethers as a route to precursors of optically active y-butyrolactones [504], An example of this sigmatropic step is given hereafter. 

A novel acid-catalysed rearrangement of 2-hydroxy-2-phenylazo-y-butyrolactone (45) to the interesting /V-substituted tetrahydro-l,3-oxazine-2,4-dione derivative (46) has been reported.58 The photo- and thermo-chemistry of diazo(2-furyl)methane and diazo(3-furyl)methane have been investigated59 using matrix isolation techniques, and 3,7-diphenylpyrano[4,3-c]pyran-l,5-diones have been prepared60 from 5,5 -diphenyl-... 

Cycloaddition to vinyl sulfoxides, y-butyrolactones/ Dichloroketene (best generated by zinc reduction of trichloroacetyl chloride, 8,156) reacts with vinyl sulfoxides to form a-dichloro-y-butyrolactones in 50 80% yield. A polar mechanism involving a Pummercr-type rearrangement has been suggested. 

Although chlorobenzene is rather inactive in usual reactions, its activity is enhanced by complex formation, and two products are formed by the reaction of stabilized carbanions on the complexed chlorobenzene 207, depending on the conditions [44], The anion of a-methy l propionitrile reacts at the meta position at —78 °C, and the mete-substituted product 208 is obtained by oxidation with I2. However, equilibration (rearrangement) of the carbanion occurs at 25 °C, because the attack of the carbanion is reversible, and the substitution product 209 of the chlorine is obtained. The fluorobenene 210, coordinated by Cr(CO)3, is very reactive. Reaction of y-butyrolactone to the o-lithiated fluorobenzene 211 gives rise to the alkoxide 212, which displaces the fluoride intramolecularly to give the cyclic ether 213 [52], In other words, the complex 211 can be regarded as the 1,2-dipolar synthon 214. However, Cr(CO)3-complexed aromatic bromide and iodide can not be used for the nucleophilic substitution. 

The sesquiterpene (+)-asteriscanolide 1 was first isolated from Asteriscus aquaticus L and characterized by San Feliciano in 1985.1 It has captured the attention of organic chemists mainly because of its uncommon bicyclo[6.3.0]undecane ring system bridged by a butyrolactone fragment. The only prior enantioselective synthesis of 1 has been described by Wender in 1988 featuring an Ni(0)-promoted [4 + 4]-cycloaddition.2 Booker-Milburn and co-workers described the sequential application of intramolecular [2 + 2]-photocycloaddition, Curtius rearrangement, and oxidative fragmentation to produce the 7-desmethyl derivative in 1997.3... 

An aluminium-catalysed tandem Claisen-ene sequence has been developed for the synthesis of homoallylic alcohols (89) and thence a-methylene-y-butyrolactones (90) in good overall yields. Extensive investigation has revealed that Et2AlSPh catalyses Claisen rearrangement of ft -substituted allyl vinyl ethers (85) into 0,5-aluminium... 

Epoxidation of exocyclic enol lactones. Peracids, even under buffered conditions, are not useful for this epoxidation because of rearrangement and decomposition. Dimethyldioxirane effects epoxidation of y-methylene-y-butyrolactones (1) in 94-96% yield in 2-3.5 hours. It is also effective for epoxidation of endocyclic enol lactones such as 3. 

Methylene butyrolactone has been used as a dipolarophile to synthesize, for the first time, ethyl-l-azabicyclo[2.2.1]hept-3-yl carboxylate using Achiwa s procedure. The synthetic pathway involves rearrangement of the spiropyrrolidine lactone resulting from the [l,3]dipolar addition.430... 

Danheiser and coworkers described a convenient preparation of oxetanones via the condensation of thioester lithium enolates with carbonyl compounds and subsequent lac-tonization under proper conditions592. The asymmetric version was reported later593, the configuration of the new chiral center being established by a stereospecific dyotropic rearrangement to the y-butyrolactone (Scheme 125)594. 

A review about the rearrangement and cycloaddition of carbonyl ylides generated from a-diazo compounds is available <2001CSR50>. Enantioselective intramolecular cyclopropanations of allyl 2-diazo-3-silanyloxybut-3-enoates to yield cyclopropyl 7-butyrolactones have been investigated with a variety of chiral rhodium catalysts. The best results were obtained with Rh2(PTTL)4, where enantioselectivity culminated at 89% ee (Equation 99) <2005TA2007>. 

Substiluled acrylic acids a-methylene-y-butyrolactones. The reaction of 1 with the allylic alcohol 2 at 170° gives the product (3) of Claisen ortho ester rearrangement. Oxidative elimination of GsHsSeOH gives the 2-substituted acrylic ester 4. 

The heating of lactones with powdered alkali cyanides leads to salts of cyano acids. The procedure is illustrated (above equation) by the synthesis of o-carboxybenzyl cyanide from phthalide and potassium cyanide (67-83%). In another instance, the reaction of potassium Cyanide with y-anisyl-y-butyrolactone involves a rearrangement thereby forming a /3-cyano acid instead of the anticipated y-cyano acid, ... 

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