摘要:
Chemical Communications NUMBER 15/1965 11 AUGUST Monohydroboration of N-Alkenylcarbamates: Preparation of Aminoalkylboronic Acids By D. N. BUTLER and A. H. SOLOWAY (Defiartment of Neurosurgery, Massachusetts Genera2 Hospital, Boston, Massachusetts 02 1 14) THE reaction of diborane with N-alkenylcarba- mates follows a similar course to that described for N-alkenylureas.1 Hydrolysis of the monohydro- borated products then affords aminoalkylboronic acids. By this method the boron analogues of )8-alanine and y-aminobutyric acid have been prepared, namely 2-aminoethylboronic acid (Ib) and 3-aminopropylboronic acid (IIb). Thus, hydroboration of ethyl and benzyl N- vinylcarbamate gave 2- (ethox ycarbonylamido) - e th ylboronic acid and 2- (benz ylox ycarbon ylamido) - ethylboronic acid respectively, while ethyl- and benzyl-N-allylcarbamates yielded mixtures with the boronic acid function in both the 2- and 3- positions to the carbamate moiety.3-Benzoxy- carbony1amido)propylboronic acid could be ob- tained pure from these mixtures. While the ethylcarbamates could not be cleanly hydrolysed, the benzyl compounds afforded the corresponding aminoalkylboronic acid hydro- bromides (Ia) and (IIa) after treatment with 10% hydrogen bromide in acetic acid. The free aminoalkylboronic acids (Ib) and (IIb) were obtained as dihydrates by ion-exchange and proved to be strong bases, indicating the possible quaterni- zation of both the boron and nitrogen atoms. The introduction of the boron atom in the non- terminal position of these allylamine derivatives, and the high yields of substituted ethylboronic acids available from the vinyl compounds, indi- cates preferred ring size of four or six atoms for the internally-stabilized borane intermediates1 in- volved.Since the yield of substituted butyl- boronic acids from hydroboration of ethyl N-3- butenylcarbamate (where a six-centred inter- mediate is possible) was less than 15% (unpublished results) a four-centred reaction intermediate may be more likely. Similar four-centred transition states have been involved to account for the cis- eliminations of the organoboranes obtained by hydroboration of vinyl chloride, and vinyl ethers and thioethers.8 (HO) ,B*CH8CH,NH8*X (I) a. X = HBr b. X = 2H80 (HO) ,BCH8CH,CH,NH,*X (11) a. X = HBr b. X = 2Ha0 (Received, May 31st, 1966; Com. 352.) 1 D. N. Butler and A. H. Soloway, J. Amer. Chem. SOL, 1964,86, 2961. H. C. Brown and 0. J. Cope, J . A*. Chm. SOC., 1964,86, 1801; D. J. Pasto and C. C. Cumbo, ibid, 1964,86, 4343.
ISSN:0009-241X
DOI:10.1039/C19650000333
出版商:RSC
年代:1965
数据来源: RSC