Bis-Lewis acids-catalyzed highly diastereoselective one-pot reductive dehydroxylation of chiral N,O-acetals

Tin Powder-Promoted Cascade Condensation/Allylation/Lactamization: Synthesis of Isoindolinones and Pyrazoloisoindol-8-ones

An efficient tin powder-promoted cascade condensation/allylation/lactamization of 2-formylbenzoic acids, hydrazides, and allyl bromides was developed for the synthesis of isoindolinones in good to excellent yields under mild conditions without any other additives or catalysts. Further manipulation of isoindolinones by iodocyclization process afforded the tricyclic tetrahydro-8 H-pyrazolo[5,1- a]isoindol-8-one derivatives, which could be converted into more complicated tetracyclic tetrahydro-4 H-azirino[1',2':2,3]pyrazolo[5,1- a]isoindol-4-ones.

Approach to Chiral 1-Substituted Isoquinolone and 3-Substituted Isoindolin-1-one by Addition-Cyclization Process

An approach to access 1-substituted isoquinolones has been developed through the addition-cyclization of imines with Grignard reagents in the presence of 2,2'-dipyridyl. A number of substituted aromatic magnesium reagents were amenable to this process, and the desired products were obtained with excellent yields and outstanding diastereoselectivities ( dr > 99:1). The utility of this convenient approach is demonstrated by the formal synthesis of ( S)-cryptostyline II. Moreover, N-methylmorpholine (NMM) was found to be an effective additive for the formation of 3-substituted isoindolin-1-ones using one-pot addition-cyclization-deprotection of imine with Grignard reagents.

A flexible asymmetric approach to methyl 5-alkyltetramates and its application in the synthesis of cytotoxic marine natural product belamide A

By using a methyl tetramate derivative (R)- or (S)-9 as a novel chiral building block, a direct, flexible, and highly enantioselective approach to methyl (R)- or (S)-5-alkyltetramates (2) is disclosed. Among the synthesized methyl 5-alkyltetramates 2, methyl 5-methyltetramate (2 a) is found in cytotoxic mirabimide E (4) and dysideapyrrolidone (5), and methyl 5-benzyltetramate (2 g) is a substructure in the potent antineoplastic dolastatin 15 (3). On the basis of this method, the first asymmetric synthesis of the antimitotic tetrapeptide belamide A (7) has been achieved in seven steps from (S)-9, with an overall yield of 23.8 %. Not only have the structure and absolute configuration of (+)-belamide A (7) been confirmed, but also the solvent used for recording the (13) C NMR spectrum, the (13) C NMR spectrum data correlation, and optical rotation data of natural belamide A (7) have been revised.