113549-23-8Relevant articles and documents
1,2-oxazines as building blocks for stereoselective synthesis: Preparation of oxygen-substituted 1,2-oxazines, either by alcohol addition or by epoxidation, and subsequent hydrogenation leading to 1,2-amino alcohols and pyrrolidines
Zimmer, Reinhold,Buchholz, Monika,Collas, Markus,Angermann, Joerg,Homann, Kai,Reissig, Hans-Ulrich
supporting information; experimental part, p. 4111 - 4121 (2010/10/02)
Stereodefined oxygen-substituted 1, 2-oxazines were prepared by three different routes. The cycloaddition of enol ethers such as 1 with a-nitrosoalkenes generated in situ gave the heterocycles 3 and 4. Acid-catalysed additions of alcohols to the 6H-1, 2-oxazines 5 led to mixtures of the adducts 6 and the substitution products 7 with moderate chemoselectivity. Epoxidation of the 6H-1, 2-oxazines 5 proceeded more efficiently and furnished the corresponding epoxides 25 and 32 in reasonable to excellent yields. It was demonstrated that the resulting oxygen-substituted 1, 2-oxazines were suitable precursors for the preparation of cyclic or acyclic primary and secondary amines in racemic or enantiopure form. Hydrogenation of the 3-phenyl-substituted 1, 2-oxazines 3 and 25a and of (6S)- and (6R)-32 preferentially furnished the 1, 2amino alcohols 15, rac-29 and (2S)- and (2R)-29. On the other hand, reduction of the 3-ethoxycarbonyl-substituted 1, 2-oxazines 4, 6d and 20 led to the formation of the N-protected proline esters 21-24 in moderate yields. It was also found that the 5-methyl-6H-1, 2-oxazine 10 was a good precursor for the propargylic ether 11, which allowed a Pauson-Khand reaction leading to the tricyclic compounds 13 and 14. Hydrogen peroxide converted 10 into a hydroperoxide intermediate, which was further transformed into the l, 2-oxazin-6-one 28b. Overall, the results demonstrate the remarkable potential of suitably substituted 1, 2-oxazine derivatives for the stereoselective synthesis of amines.
Peracid Oxidation of 4-Isoxazolines as a Method for the Preparation of α, β-Unsaturated Carbonyl Compounds
Padwa, Albert,Chiacchio, Ugo,Kline, Donald N.,Perumattam, John
, p. 2238 - 2245 (2007/10/02)
A study of the MCPBA peracid oxidation of a series of 4-isoxazolines has been carried out.A variety of isoxazolines were synthesized by treating nitrones with electron-deficient alkynes.An alternate approach involves dipolar cycloaddition of nitrones with activated allenes followed by a subsequent base-catalyzed isomerization of the initially formed cycloadduct.Treatment of the 5-exo-methyleneisoxazolidine derived from the reaction of N-benzylidenemethylamine N-oxide and (phenylsulfonyl)propadiene with LDA followed by γ-alkylation also produced substituted 4-isoxazolines.The peracid oxidation of the isoxazoline ring afforded α,β-unsaturated carbonyl compounds in excellent yield.Reductive cleavage of the sulfonyl group of some of the enones was achieved by initial protection of the carbonyl functionality by cyanosilylation using trimethylsilyl cyanide, and this was followed by aluminum-amalgam reduction.The cycloaddition-oxidation procedure provides an attractive route to synthesize α,β-unsaturated ketones since it avoids acidic or basic conditions.
