Carbamates Allyl chloroformate

Carbamates Allyl chloroformate, 9 Boron trifluoride etherate, 43 t-Butyldimethylsilyl trifluoromethanesul-fonate, 50... 

Allyl chloroformate, CH2CI2, >80% yield." In this case, the benzylamine was converted to an alloc carbamate. 

Reaction of ethyl chloroformate with allylamine to give ethyl allyl-carbamate [30]. 

The cyclohexene 121, which was readily accessible from the Diels-Alder reaction of methyl hexa-3,5-dienoate and 3,4-methylenedioxy-(3-nitrostyrene (108), served as the starting point for another formal total synthesis of ( )-lycorine (1) (Scheme 11) (113). In the event dissolving metal reduction of 121 with zinc followed by reduction of the intermediate cyclic hydroxamic acid with lithium diethoxyaluminum hydride provided the secondary amine 122. Transformation of 122 to the tetracyclic lactam 123 was achieved by sequential treatment with ethyl chloroformate and Bischler-Napieralski cyclization of the resulting carbamate with phosphorus oxychloride. Since attempts to effect cleanly the direct allylic oxidation of 123 to provide an intermediate suitable for subsequent elaboration to ( )-lycorine (1) were unsuccessful, a stepwise protocol was devised. Namely, addition of phenylselenyl bromide to 123 in acetic acid followed by hydrolysis of the intermediate acetates gave a mixture of two hydroxy se-lenides. Oxidative elimination of phenylselenous acid from the minor product afforded the allylic alcohol 124, whereas the major hydroxy selenide was resistant to oxidation and elimination. When 124 was treated with a small amount of acetic anhydride and sulfuric acid in acetic acid, the main product was the rearranged acetate 67, which had been previously converted to ( )-lycorine (108). 

Finally, Scheme 8.222 exemplifies the transprotection of an N-allyl indoline to the corresponding ethyl carbamate using ethyl chloroformate and sodium iodide.44 Use of the chloroformate alone requires very long reaction times, but added sodium iodide generates the more reactive iodoformate. 

Primary allylic amines. Aziridines can be converted into allyl carbamates by reaction with ethyl chloroformate to form N-ethoxycarbonylaziridines followed by thermolysis in benzene at 200-250°, Rearrangement of trisubstituted ethoxycarbonylaziridines is regiospecific. 

Heating of the benzene solution of 44 and K2CO3 induced the intramolecular Sn2 reaction to afford 6-deoxycodeine 45 in 53% yield (Scheme 10). The major side product in this reaction was, as anticipated, diene 46 (30% yield), which was formed by elimination reaction. It was reported that the solvent effect is significant in the Sn2 reaction when this reaction was carried out in acetonitrile, diene 46 was obtained as the major product. Treatment of 45 with methyl chloroformate provided a methyl carbamate, whose allylic oxidation with Se02 in the presence of f-BuOOH introduced the hydroxy group at C-6 to give 19. PCC oxidation of 19, followed by LiAlH4 reduction, provided racemic codeine. 

A number of allyl carbamates have been synthesized from the corresponding chloroformates with amino compounds [408]. 

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