Synthesis of phthalides
A surprisingly facile conversion of 2-formyl-arylketones into 3-substituted phthalides generally proceeds smoothly in DMSO, either in a Cannizarro-Tishchenko-type reaction under nucleophile catalysis (NaCN) or under photochemical conditions (DMSO, 350 nm).
D. C. Gerbino, D. Augner, N. Slavoy, H.-G. Schmalz, Org. Lett., 2012, 14, 2338-2341.
An electrochemical C(sp3)-H lactonization of 2-alkylbenzoic acids provides phthalides by utilizing a graphite anode, dichloromethane as solvent, hexafluoroisopropanol as cosolvent, and n-Bu4NClO4 as electrolyte. This simple, intuitive, and atom-economical protocol enables the synthesis of various phthalides and other 5- and 6-membered lactones in good yields.
J. E. Hong, J. Yoon, W. Baek, K. Kim, J.-H. Kwak, Y. Park, Org. Lett., 2023, 25, 298-303.
A palladium-catalyzed arylation of aldehydes with organoboronic acids gave 3-arylphthalides in good to excellent yields with high substrate tolerance in the presence of a thioether-imidazolinium carbene ligand.
M. Kuriyama, N. Ishiyama, R. Shimazawa, R. Shirai, O. Onomura, J. Org. Chem., 2009, 74, 9210-9213.
A new diamine ligand for Ru-catalyzed asymmetric transfer hydrogenation (ATH) enabled a highly enantioselective reduction of 2-acylarylcarboxylates. Subsequent in situ lactonization under aqueous conditions provided efficient access to a various 3-substituted phthalides in enantiomerically pure form.
B. Zhang, M.-H. Xu, G.-Q. Lin, Org. Lett., 2009, 11, 4712-4715.
Cobalt-catalyzed intramolecular hydroacylations of 2-acylbenzaldehydes and 2-alkenylbenzaldehydes afford phthalide and indanone derivatives, respectively, in good yields with high enantioselectivities in the presence of chiral diphoshines.
J. Yang, N. Yoshikai, J. Am. Chem. Soc., 2014, 136, 16748-16749.
A rhenium-catalyzed C-H activation enables a [4 + 1] annulation of a broad range of benzamides with aldehydes to provide phthalides.
B. Jia, Y. Yang, X. Jin, G. Mao, C. Wang, Org. Lett., 2019, 21, 6259-6263.
Pd catalysis enables an efficient synthesis of a broad range of isobenzofuran-1(3H)-ones from o-bromobenzyl tertiary/secondary/primary alcohols.
L. Mahendar, G. Satyanarayana, J. Org. Chem., 2016, 81, 7685-7691.
An efficient domino one-pot strategy for the synthesis of isobenzofuran-1(3H)-ones includes [Cu]-catalyzed intermolecular cyanation of o-bromobenzyl alcohols, in situ intramolecular nucleophilic attack and hydrolysis. This reaction can successfully be carried out under environmentally benign conditions, using water as sole green solvent.
L. Mahendar, G. Satyanarayana, J. Org. Chem., 2015, 80, 7089-7098.
Mild Au(I)- and Pd(II)-catalyzed SN2' reactions of readily prepared allylic alcohols enable a convenient strategy for the synthesis of phthalides and γ-butyrolactones. Using these catalysts, exclusive formation of the desired five-membered lactones is observed without formation of undesired seven-membered rings via competing direct lactonization pathways.
J. Liu, R. J. Miotto, H. Segard, A. M. Erb, A. Aponick, Org. Lett., 2018, 20, 3034-3038.
A modified Julia olefination enables a highly stereoselective synthesis of exo-enol esters from cyclic anhydrides. A subsequent one-pot Smiles rearrangement gives a straightforward access to exo-enol lactones. Furthermore, the reaction was extended to semistabilized sulfones and applied to the synthesis of maculalactone B.
N. Dussart, H. V. Trinh, D. Gueyrard, Org. Lett., 2016, 18, 4790-4793.
A highly efficient palladium(0)-catalyzed strategy for the synthesis of isocoumarins involves cyclization with incorporation of tert-butyl isocyanide followed by simple acid hydrolysis to provide valuable lactones in good yields. The methodology is tolerant of a wide range of substrates and applicable to library synthesis.
X.-D. Fei, Z.-Y. Ge, T. Tang, Y.-M. Zhu, S.-J. Ji, J. Org. Chem., 2012, 77, 10321-10328.
A palladium-catalyzed C-H activation enables a selective O-cyclization of N-methoxy aryl amides with CH2Br2 or 1,2-dichloroethane. The reaction forms C(sp3)-O and C(sp2)-C(sp3) bonds simultaneously with the assistance of an N-methoxy amide group and tolerates various functional groups.
W.-H. Rao, L.-L. Jiang, J.-X. Zhao, X. Jiang, G.-D. Zou, Y.-Q. Zhou, L. Tang, Org. Lett., 2018, 20, 6198-6201.