Pyrroline-2-carboxylic acid esters

Potassium tert-butanol Pyrrole-2-carboxylic acid esters from tosylglycine esters via 3-hydroxypyrrolidine- and J -pyrroline-carboxylic acid esters... 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

Poly(vinyl acetate), PVAc, of molecular weights (M ) 6.1x1 01, 1.9xl05, and 6.0xl05, was randomly labeled by ester exchange with 2,2,5,5-tetramethyl-3-pyrrolin-l-oxyl-3-carboxylic acid to give a spin labeled polymer containing typically 1-10 nitroxides per polymer molecule. Polystyrene was prepared by emulsion... 

The reactivity of the a-methylene group in lactams allows Claisen condensation with esters of formic, oxalic, and arylcarboxylic acids. Treatment of ethyl formate with A-methylpiperidone, followed by acidification, yields a salt of 1 -methyl- J2-piperideine, whereas in an alkaline medium its dimer was isolated.34- 158 With oxalic acid ester as the condensing reagent, 1-methyl-J2-pyrroline-2-carboxylic acid159 and l-methyl-d2-piperideine-2-carboxylic acid160 were obtained (Scheme 4). 

Decarboxylation with concomitant dehydrogenation occurred in some cyclic amino acids. For example, (I)-proline was converted into a mixture of 1-pyrroline and its trimer. The methyl ester of (L)-proline was simply dehydrogenated to its /i-imine (69%). With two equivalents of IOB in chloroform (L)-proline was converted directly into 2-pyrrolidinone (70%). This transformation was less efficient for pipecolinic acid and ( )-pyrrolidinone-5-carboxylic acid [48]. 

In the presence of Rose Bengal as sensitizer and under either aerobic or anaerobic conditions, proline is photodecarboxylated to A -pyrroline, and under similar conditions the methyl ester yields an equimolar mixture of A -and A -pyrroline-2-carboxylic acid methyl esters. These observations suggest that the reaction proceeds by a Type I photooxidation. 

Lysine-labelled tryptophanase was prepared by Incubating the enzyme with 100-fold molar excess of 2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl-3-carboxylic acid N-hydroxysuccinimide ester (Eastman Kodak Company) in 10 mM bis-tris-propane (Sigma), pH 8 (20% v/v... 

Phosphonium chloride 2 is readily hydrolyzed in alkaline medium giving cyclopropanecarb-oxylic acid (4), while the phosphonium tetrafluoroborate 3 is an excellent reagent, for the cycloalkenylation of carbonyl compounds, e.g. -0x0 esters, or can be utilized for the construction of functionalized 2-pyrrolines (e.g. 7) from imides. A similar reaction with the sodium salts of cyclic imides gives access to ethyl l,2,5,6-tetrahydro-3-oxo-3//-pyrrolizine-7-carboxylate (6, n = 1) and ethyl 2,3,5,6,7,8-hexahydro-5-oxoindolizinecarboxylate(6, n = Other transformations include the conversion into 2,3-dihydrofurans 8" and spiroketo ester... 

Acid-mediated hydrolysis of 5-halopyrrole-2-carboxylates provides access to 5-carboxy-3-pyrrolin-2-ones, but this transformation often lacks the regioselectivity of other methods. This reaction was first reported by Siedel (1943LAC144). In a more recent example, Battersby and coworkers have treated 5-bromopyrrole-2-carboxylate 548 with sulfuric add in methanol, and a mixture of 3-pyrrolin-2-ones 549 and 550 was obtained in low yield (Scheme 156 1988PT(1)1557). These reaction conditions led to both hydrolysis of the bromine and deprotection of the <-butyl ester followed by decarboxylation. In a related reaction involving a symmetrical substrate, Lugtenberg and de Groot converted 5-bromo-2-trichloroacetyl-3,4-dime-thylpyrrole into 3,4-dimethyl-3-pyrrolin-2-one via treatment with NaOH (1982MI2). 

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