Benzoxazines, construction

A similar construction of 2H- 1,3-benzoxazines employs salicylamide and dialkyl ketones the product benzoxazinones (166) can be converted into alkoxy (167 R = alkoxy) or chloro (167 R2 = Cl) derivatives by alkylation (32CB1032), or by treatment with phosphorus oxychloride (80CPB465) respectively (Scheme 58). 

The first total synthesis of ( )-obscurinervidine (50) (309) starts essentially from the benzoxazine 524, which was prepared from pyrogallol. Construction of the pyrrole ring on the IV-amino derivative of 524 gave, after... 

A standard way of synthesizing 1,3-benzoxazines is to react 2-hydroxybenzylamines with aldehydes or ketones <88JCS(P2)46l> this approach is exemplified by a construction of pyrazolo[2,3-... 

Reaction of phenols and hexahydro-l,3,5-triazines at 150°C also provides access to dihydro-1,3-benzoxazines (272) (Equation (24)). Similar constructions use hexamethylenetetramine, rather than hexahydro-l,3,5-triazines, but now the products are 3-benzyl derivatives (e.g. 273) (Equation (25)) <85ZOR2243>. It seems likely that, in these reactions, the nitrogen-containing reagents act as sources of methylenimine, which convert the phenols into the corresponding benzylamines. Further reactions with more methylenimine then results in cyclization if so these preparations are closely related to those which employ hydroxybenzylamines and carbonyl compounds. 

The pyrazino[2,l-c][l,4]benzoxazine (322 X = 0) was synthesized from 3-(aminomethyl)-benzoxazine (321 = NH2) (Scheme 24). The piperazine ring was constructed by alkylation with... 

A new oxidative ring-closure carboarylation of ortho-ethynyl anilides 2-(RC0NH)C6H4C=CR with diaryliodonium salt ArAr f OTf, catalysed by (TfO)2Cu, has been developed as a method for the construction of benzoxazines bearing a fiilly substituted exo-double bond. The reaction proceeds via an unusual 6-exo-dig cyclization step with the formation of C-O and C-C bonds in an onh -manner. ... 

In continuation to the above strategy, diaryliodonium salts were also used by Sinai et al. for the construction of benzoxazines 154 (Scheme 36). It was achieved by the reaction of O-ethynylanilides 153 with diaryliodonium salts in the presence of copper triflate as a catalyst. The mechanism of oxidative transformation is likely to be an unusual 6-endo-dig cyclization which resulted in new C-O and C-C bonds formation [52]. 

N. Bodipati, R.K. Peddinti, Chemical generation of o-quinone monoimines for the rapid construction of 1,4-benzoxazine derivatives, Org. Biomol. Chem. 10 (2012) 1958-1961. 

Gallagher et al. reported on various IV-heterocycle construction via cyclic sulfamides. Using this strategy, they synthesized enantiopure 1,4-benzoxazine 311, which was the precursor of the blockbuster antibiotic levolloxacin 312 (Scheme 40.67). Starting from Boc-protected amino alcohol 305, sulfamidate 306 was prepared using RuCU and NaI04. 306 was treated with halo phenol 308 followed by acidic hydrolysis to afford amino ether 310. The compound 310 underwent Pd-catalyzed C—N alkylative cyclization to produce benzoxazine 311, which was the potential precursor from which Levolloxacin 312 can be synthesized. 

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