Y-butyrolactoncs

Pyrolysis of the ethylene acetal of bicyclo[4.2.0]octa-4,7-diene-2,3-dione yields a-(2-hydroxyphenyl)-y-butyrolactonc 11 a mechanism involving a phenyl ketene acetal is proposed. Tartrate reacts with methanediol (formaldehyde hydrate) in alkaline solution to give an acetal-type species (9) 12 the formation constant was measured as ca 0.15 by H-NMR. Hydroxyacetal (10a) exists mainly in a boat-chair conformation (boat cycloheptanol ling), whereas the methyl derivative (10b) is chair-boat,13 as shown by 1 H-NMR, supported by molecular mechanics calculations. 

Stable A-phosphino- and A-phosphonio-nitrilimincs 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, /J-dimcthyl- y-butyrolactonc, has been reported.102 The 1,3-dipolar cycloaddition of A, A -diarylbisnitrilc 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... 

Dipolar aprotic organic solvents, e.g., acetonitrile, tetrahydrofurane, dimethylformamide, dimethylsulfoxide, sulfolane, methylene chloride, y-butyrolactonc, etc ... 

Enantiospecific addition to chiral vinyl sulfoxides. The cycloaddition of dichloroketene (11, 169-17(1) to optically pure (R)- or (S)-l-cyclohexenyl tolyl sulfoxides (1) leads to optically pure y-butyrolactoncs (2) with complete cnantiospecificity at the two chiral centers. A third hiral ew-center is introduced in the addition of monochloroketene. 

For the conversion of c/.v-fused lactones into a-mcthylcne-y-butyrolactoncs, see 1,2-Dibromoethane, this volume. 

Star-shaped polylactones with functional end groups via ring-expansion polymerization of f-caprolactone or y-o,i-butyrolactonc with a spiroinitia-tor was synthesized as shown in Fig. 44 [146]. The spirocyclic polylactones formed were reacted with various carboxylic acid chlorides and yielded fourarmed stars with the elimination of Bu2SnCl2. Star arms with chloroacetate, 4-bromobenzoate, 4-nitrobenzoate, cinnamate, stearate, or methacrylate end groups were obtained by varying the acid chlorides. 

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