Dihydro-oxazines, preparation

Dihydro-l,3-4//-oxazines (32) are among the best known 1,3-oxazines. Their preparation was first described by Gabriel and Elfeldt in 1891. The reaction consisted in benzoylation of y-bromopropyl-amine in the presence of sodium hydroxide by an intermediate formation of A"-benzoyl-y-bromopropylamine (31). The cyclization of the... 

Abstract 2,4-Disubstituted-3,4-dihydro-2/f-naphth[2,l-e][l,3]oxazines were prepared through the ring-closure reactions of the starting aminonaphthols with substituted aromatic and hetaryl aldehydes. 

Dihydro-4//-l,2-oxazines are prepared by [4 4- 2] cycloaddition of nitrosoalkenes to electron-rich olefins1,2. 

Dihydro-4//-1,2-oxazines are prepared by the cycloaddition of nitrosoalkenes and alkenes CH2 = C(NO)COMe with trans-stilbene gives (101) (78CC847). 

A number of 2-aryl and 2-alkyl derivatives of 5,6-dihydro-l,3-4i/-oxazine have been prepared in a similar An analogous re-... 

The only known derivative of this class was prepared from ethyl 8-anilinecrotonate, ethyl acetoacetate, and benzaldehyde. In the first instance, a pyrimidine derivative is formed, this is then subjected to partial hydrolysis to form the 3,4-dihydro-l,3-2H-oxazine derivative (42). 

When an S-alkyl-A A -disubstituted isothiourea reacts with diketene in a boiling solvent, 2-imino-4-keto-3,4-dihydro-l,3-2i/-oxazine derivatives (45) are formed. Analogous compounds can be prepared from dialkylcarbodiimides and diketene. ... 

We are the first group to succeed with the highly enantioselective 1,3-dipolar cycloadditions of nitronates [75]. Thus, the reaction of 5,6-dihydro-4H-l,2-oxazine N-oxide as a cyclic nitronate to 3-acryloyl-2-oxazilidinone, at -40 °C in dichloro-methane in the presence of MS 4 A and l ,J -DBFOX/Ph-Ni(II) complexes, gave a diastereomeric mixture of perhydroisoxazolo[2,3-fe][l,2]oxazines as the ring-fused isoxazolidines in high yields. The J ,J -DBFOX/Ph aqua complex prepared from... 

A synthesis of aldehydes developed by Meyers begins with the commercially available dihydro-1,3-oxazine derivatives 132 (A = H, Ph, or COOEt). Though the ions (133) prepared from 132 are ambident, they are regioselectively alkylated at... 

The only salt of this type was prepared by refluxing of tV-methylimidazole with 3-bromomethyl-6,6-dimethyl-4-phenyl-5,6-dihydro-4//-oxazine in toluene for 5h (473). 

Optically pure 2,3-dihydro-6//-l, 4-oxazin-2-ones were prepared in a two-step reaction from A-protected AAs and a-bromoketones (78JOC135). When heated in boiling toluene and HCl 2,2-dimethylamino acid amides were transformed into the corresponding 3,3-dimethyl-l,4-oxazine-2,5-diones (83TL1921 87HCA329). 

The simplest method for the preparation of dihydro-1,3-oxazines is the cyclization of the corresponding stereoisomeric 1,3-amino alcohol with imi-dates, or acylation of the amino alcohols and subsequent cyclization. 

Due to the restricted availability of nitroso components, it more convenient to prepare acylnitroso compounds in situ from iV-acyl or Af-carbamoyl hydroxylamines with NaI04 (equation 100) . Subsequent deprotection results in an Af-unsubstituted dihydro-1,2-oxazine cycle. The reaction is also commonly employed for intramolecular cyclo-additions ". ... 

This technique may also be modified to prepare acetaldehyde derivatives by use of 2,4,4,6-tetramethyl-5,6-dihydro-l,3(4H)-oxazine1 2 3 4 5 6 7 and 2-carboethoxy acetaldehydes using 2-(carbo-ethoxymethyl)-4,4,6-trimethyl-5,6-dihydro-l,3(4H)-oxazine.3 Functionalized aldehydes and dialdehydes may also be obtained by suitable modification.8 Generally, the intermediates can be used without purification and the overall yields of the aldehydes range from 50-70%. 

The asymmetric alcoholytic ring opening of 4-substituted-2-phenyl-4,5-dihydro-l,3-oxazin-6-ones proved to be a efficient method for the preparation of enatiomerically pure /3-amino acid derivatives <2005AGE7466>. Treatment of 2,4-diphenyl-4,5-dihydro-l,3-oxazin-6-one 208 in the presence of the bifunctional chiral thiourea catalyst 211 resulted in formation of an enantiomerically enriched mixture of the unchanged oxazinone (iJ)-208 and allyl (4)-3-benzoyl-amino-3-phenylpropanoate 209. The resolved material (iJ)-208 and the product 209 could easily be separated by a selective hydrolytic procedure that converted oxazinone (iJ)-208 quantitatively into the insoluble iV-benzoyl /3-amino acid 210 (Scheme 37). 

In the condensation of /3-hydroxy aldehydes 303 with A -sulfonyl aliphatic aldimines 304 (which could also be prepared in situ from the aliphatic aldehyde and A -sulfinyl /i-toluenesulfonamide), 2,5,6-trisubstituted 3,6-dihydro-277-1,3-oxazines 306 were formed as single /ra r-stereoisomers (Scheme 57). No oxazine formation was observed in the... 

A convenient, one-pot procedure devised for the preparation of 2-phenyl-5,6-dihydro-4//-l,3-oxazine 373 was based on the A -bromosuccinimide oxidation of tetrahydro-l,3-oxazine 372, formed in situ from 3-aminopropanol 371 and benzaldehyde (Scheme 69) <2006S2996>. 

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