Chiral oxaziridines in the enantioselective synthesis of isoxazolidines

Diastereoselective C-alkylation of aldimines, derived from chiral α-carbon heteroatom-substituted aldehydes, with triethylborane. Application to the synthesis of benzylisoquinolines

The one-pot reaction of a chiral aldehyde, p-methoxyaniline or p-fluoroaniline, and triethylborane produces the corresponding alkylated chiral amine with high yields and diastereoisomeric ratios. Stereocontrol is induced by the presence of a heteroatom in the α-position to the aldehyde. In the case of alkylation of imines derived from chiral aliphatic amines, good yields and moderate to high diastereoselectivity are obtained: yields are significantly better when the preformed imine is used in the reaction with triethyl borane, and diastereoselectivity of the reactions largely depends on the structure of the chiral aliphatic amine. The methodology is successfully applied to the synthesis of romneine, a natural benzylisoquinoline.

Macrocyclic and polymeric oxaziridine-derivatives

Macrocyclic and polymeric imines 5,5' and 6,6' are obtained in excellent yields by template-free polycondensation of 1,6-bis(4-formylbenzoyloxy)hexane (1) with commercially available 4,4'-methylene-bis(cyclohexylamine) (2) and with bis(2-amino-2-methylprop-1-yl)adipate dihydrochloride (4), respectively. The degree of macrocyclization during imine synthesis strongly depends on the diamine. Matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry analysis and gel permeation chromatography (GPC) measurements show that (2) leads to more macrocyclic adducts than (4). The subsequent meta-chloroperoxybenzoic acid oxidation of polyimines 5,5' and 6,6' ($ \bar M_{\rm n} $ = 1650-11 200 g mol(-1) , $ \bar M_{\rm w} $ = 3800-27 350 g mol(-1) ) yields the corresponding polyoxaziridines 7,7' and 8,8' consisting of macrocyclic and linear polymeric structures ($ \bar M_{\rm n} $ = 1750-8050 g mol(-1) , $ \bar M_{\rm w} $ = 3250-15 800 g mol(-1) ). The synthesized polyoxaziridines are relatively stable and storable at room temperature.

Poly(1,2,4-oxadiazolidin-5-one)s synthesized by polycycloaddition of bisoxaziridines and diisocyanate

A premier in polymer chemistry: the cycloaddition of bisoxaziridines with 4,4'-methylene diphenyl diisocyanate yields novel linear poly(1,2,4-oxadiazolidin-5-one) derivatives. The polymers are relatively stable (>200 °C) and model reactions show that the reaction rate strongly depends on the electronic properties of the oxaziridine unit; electron-donating substituents on the C atom of the heterocyclic ring promote the cycloaddition.

Synthesis of dihydrobenzisoxazoles by the [3 + 2] cycloaddition of arynes and oxaziridines

Dihydrobenzisoxazoles are readily prepared in good yields by the [3 + 2] cycloaddition of oxaziridines and arynes. The reaction involves an unusual cleavage of the C-O bond of the oxaziridine and tolerates a variety of substituents on the oxaziridine and the o-(trimethylsilyl)aryl triflate to form aryl-, heteroaryl-, alkyl-, and naphthyl-substituted dihydrobenzisoxazoles. The resulting halogen-substituted dihydrobenzisoxazoles are readily elaborated to more complex products using palladium-catalyzed crossing-coupling processes.