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Steric carbonyl protection metalation and cleavage of highly hindered ureas. Preliminary communication
Author(s) -
Hassel Tillmann,
Seebach Dieter
Publication year - 1978
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19780610625
Subject(s) - chemistry , steric effects , piperidine , dimethylamine , phosgene , metalation , medicinal chemistry , butyllithium , amine gas treating , toluene , organic chemistry , ring (chemistry) , benzene
Ureas of type 3 with sterically protected carbonyl groups such as 4a‐7a are prepared by successively adding 2 equivalents of a highly substituted sec. amine and an excess of dimethylamine to benzene or toluene solutions of phosgene. The piperidine derivatives 6a and 7a are metalated in high yields to 6b and 7b , respectively, with sec. ‐butyllithium/TMEDA in THF at 0° [see derivatives 6, 7 , ( c‐i ) in Table 1 ]. Methods of cleaving urethanes 2 (see 8 → 9 ) and ureas 3 are described, among which the retro‐Mannich reaction, removing the piperidine ring from 7 under acidic hydrolysis conditions, appears to be promising also for other applications of sterically blocked carbonyl compounds in organic synthesis.