Butyrolactones cycloaddition

The stereoselective [2+2] cycloaddition between ketenes and enolethers can be used as a key step in the construction of y-butyrolactones (Scheme 14) [45], if the resulting cyclobutanones can subsequently undergo ring enlargement by a regioselective Baeyer-Villiger oxidation. 

This cycloaddition-reduction-hydrolysis sequence was also used in an approach to butyrolactones related to ribonolactone (71). These compounds are inducing agents of hunger and satiety in mammalians. Here, a subsequent aldol 1,3-diol reduction was used, and the required carboxy function was established by oxidation of the aromatic ring with ruthenium tetroxide. Cycloaddition of benzonitrile oxide to allyl alcohol afforded an enantiomeric mixture of isoxazolines 55 and 56, which were treated with sodium hydride and methyl iodide to achieve separation by chromatography on cellulose triacetate (71). 0-Demethylation, followed by... 

Cycloadditions to exocyclic C=C bonds have been carried out for ot-methylene-butyrolactones (254) (154,155), 4-methylenepyrazol-3-ones (255) (156), 4,5-dihy-dro-5-methylene-17/-pyrazoles (256) (157), 4,5-dihydroisoxazoles (257) (158),... 

The chiral acrylate 164 was used in a 1,3-dipolar cycloaddition with a nitrile imine. Bis(trityl)nitrile imine was found to undergo a diastereoselective 1,3-dipolar cycloaddition with (f )-a-(acyloxy)-p,p-dimethyl-y-butyrolactone 164 to give the 2-pyrazoline product with a de of 50% (Scheme 12.51) (275). 

A new Y solvolysis scale has been developed for benzylic species with extensive charge delocalization, based upon the solvolyses of some benzhydryl bromides and /-butyl(2-naphthyl)methyl bromides.39 Chlorides have negative salt effects on the ionization of benzhydryl bromide in 7-butyrolactone.40 The X-ray structure of the dimerization product of l,8-bis(dhnethylammonio)-4-naphthyl(phenyl)methyl carbocation has been determined it appears to be formed via a 4n + 2n-cycloaddition mechanism 41... 

Stable /V-phosphino- and /V-phosphonio-nitrilimines undergo 3 + 2-cycloaddition with electron-poor and electron-rich dipolarophiles, respectively, to produce substituted pyrazolines.101 The first diastereoselective 3 + 2-cycloaddition between bis(trityl)ni-trilimine and an acrylate, (R)-a-(acryloxy)-/f, jS-dimethyl-y-butyrolactone, has been reported.102 The 1,3-dipolar cycloaddition of A, A -diarylbisnitrile imides with cinnamonitriles produces exclusively 5, 5 -dicyano-4,4, 5, 5 -tetrahydro[3, 3 -di-l//-pyrazoles] which yield the corresponding 3,3 -di-l//-pyrazoles on thermal aromatization.103... 

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. 

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... 

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>. 

Enantiospecific addition to chiral vinyl sulfoxides.3 The cycloaddition of dichloroketene (11, 169-170) to optically pure (R)- or (S)-l-cyclohexenyl tolyl sulfoxides (1) leads to optically pure y-butyrolactones (2) with complete enantiospecificity at the two chiral centers. A third chiral exo-center is introduced in the addition of monochloroketene. 

The ketenimine (93) reacts only at the C=N bond to give pyrroles and pyrrolines with methylene migration (equations 102,103). Carbon (hoxide codimerizes smoothly with methylenecyclopropanes to yield lactones with alkene isomerization (equations 104, lOS). The Pd -catalyzed rearrangement of y-butyrolactone (94) to butenolide (95) indicates that this CO2 insertion reaction is reversible. Hiis is fur-ter supported by the observation that lactone (94) can serve as a TMM precursor in the codimerization with aldehydes and electron-deficient alkenes (equations 106, 107). No cycloaddition to ketenes or simple ketone carbonyls has ever been reported. 

With an acceptor-substituted alkene moiety tethered to the molecule, the intermediate silyl enol ether may undergo an intramolecular [2-I-2] cycloaddition.The silyl-assisted addition of hydrogen halides to cyclopropanes is not restricted to ketones with carbonyl groups as activating function or iodide as nucleophile. Esters and other acid derivatives underwent similar reactions when treated with iodotrimethylsilane alone or in the presence of an additional catalyst such as mercury(II) or zinc(II) chloride.Subsequent treatment of the y-iodo ester with potassium carbonate in tetrahydrofuran gave the respective y-butyrolactones in good yield. 

For reasons not as yet totally understood, the c r/o-cycloaddition product is predominantly formed endojexo 87.6 12.4) in the palladium(0)-catalyzed reaction involving a more complex substrate, i.e. the cyclopentaannulated butyrolactone (5,5)-23. The diastereomeric mixture of the [3-1-2] cycloadducts 24 is formed in 75% yield. ... 

In attempts to promote the acid-catalyzed intermolecular Diels-Alder reactions of the acylimine 24 with neutral dienes the predominate formation of a-acylamino-S-alkenyl-8-butyrolactones was observed. It has been suggested that the major products are derived from the 4n participation of the acyliminium salts in a [4+ + 2] cycloaddition with the dienes followed by a subsequent acid-catalyzed rearrangement to the observed products [Eq. (79)].172... 

Systematic studies have shown that intramolecular [2+2] cycloadditions of unsaturated ketenes or ketiminium salts (278) constitute a simple and reasonably general approach to cyclobutanones (279), which are useful as precursors to butyrolactones following Baeyer-Villiger oxidation. The potential of this method is clearly shown by the efficient formation of the bicyclo[5.2.0]nonane (280) and of the... 

A number of examples such as 1,3-dioxanes, macrolactones, °° ring-containing biaryls, ° spirooxindoles, alkaloid-like compounds, and polycyclic compounds from the Schreiber group illustrate this approach to natural product-like libraries (see Chapter 11). An early example converted shikimic acid into intermediate tetracyclic y-butyrolactones, which were then functionalized around the core structure (see Chapter 11, Subsection 11.10.2). y-Butyrolactones, found in about 10% of all natural products and which exhibit a broad range of biological activities, are a key element in a number of recent natural product-like compounds. A more recent example, inspired by the rich skeletal diversity of indole alkaloids, utilized the rhodium(II)-catalyzed consecutive cyclization-cycloaddition reactions developed by Padwa and coworkers (Scheme 1.4). A stereocontrolled tandem reaction utilizing the versatile scaffold allowed for multiple modes of intramolecular reactions. 

Chatani N, Tobisu M, Asaumi T, Fukumoto Y, Murai S (1999) Ruthenium carbonyl-catalyzed [2- -2- -l]-cycloaddition of ketones, olefins, and carbon monoxide, leading to functionahzed y-butyrolactones. J Am Chem Soc 121 7160-7161... 

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