Carbamates halocyclization

Halocyclization via A -Carbamates in Cyclic Systems Synthesis of Bicyclic 2-Oxazolidinones... 

The halocyclization of a homoallylic carbamate 718, containing (S)-l-phenylethylamine as chiral source, similarly affords a 50 50 diastereomeric mixture of tetrahydro-2//-l,3-oxazin-2-ones 8, which can be easily separated by chromatography and identified by 1 H-NMR spectroscopy. In compounds 8, the substituent at C-6 displays a strong tendency to occupy the equatorial position in both isomers. 

The 6(Oy "-endo- g halocyclization of propargylic carbamates R C=CCH(R )-NHC02Bn, promoted by I2, Br2, and CI2, resulted in the formation of 5-halogeno-l,3-oxazin-2-ones the 5-endo-dig cyclization that would give rise to the isomeric oxazolidinones has not been observed. The results were rationalized by calculations at the B3LYP/6-31IG level. ... 

Carbamates also participate in analogous cyclizations as demonstrated in Ohno s synthesis of the antibiotic (-t-)-negamycin (227, Scheme 9.30) [168]. Halocyclization of N-silylated carbamate 225 proceeded with higher trans selectivity dr =93 7) relative to the analogous cyclization of the corresponding unprotected carbamate. 

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See also in sourсe #XX -- [ ]

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