摘要:

The condensation between 2,6-dinitrobenzaldehyde and a pyrrole does not afford a dipyrrylmethane but products which result from a duplication of the starting pyrrole or from oxydo-reduction reactions of the pyrryl-arylcarbinol9which arise from the condensation between one molecule of pyrrole and one molecule of aldehyde. The nitro groups of the benzaldehyde play a crucial role in these reactions.

ISSN:0008-4042    

DOI:10.1139/v84-352

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Carboxylic acids, alcohols (R′OH), and alkanes (R′H) are the main products of the reduction of carboxylic esters (RCO2R′) by sodium in hexamethylphosphoric triamide (HMPA). Alkanes are preferentially formed from the carboxylic esters of hindered alcohols. The alkane content, however, is lowered when there is less steric hindrance on the carboxylic group, and increased whentert-butanol is introduced into the reaction mixture. The reduction of esters in HMPA has been compared to the reduction in alkylamines. The alkane is produced mainly by the decomposition of a radical anion intermediate which can be solvated by HMPA. The alcohol is the result of several possible bimolecular nucleophilic reactions; however, unimolecular and bimolecular processes are involved in the production of the carboxylic acid.

ISSN:0008-4042    

DOI:10.1139/v84-353

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

For reactions of 2,2-dibromocyclopropyl carboxylic acids with methyllithium, the course of reaction depends mainly on the position of the carboxyl group. When the COOH group is directly attached to thegem-dibromocyclopropane ring MeLi generally attacks thegem-dibromo moiety and gives the corresponding monobromocyclopropane as the principal product. When the reaction is performed above −80 °C the monobromides are formed stereospecifically in thetransconfiguration. The highest yields, as high as 80–90%, are obtained at 0 °C. When the carboxyl group is not directly attached to the cyclopropane ring most of the MeLi is consumed in an acid–base reaction with the COOH group.

ISSN:0008-4042    

DOI:10.1139/v84-354

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Experiments with intact callus cultures ofAndrographispaniculataand a derived cell-free system have established that: (1) the biosynthesised γ-bisabolene has theZ-configuration6; (2) the biosynthetic intermediate is a 6-trans-13and not a 6-cis-15farnesyl pyrophosphate; (3) in paniculide B17, and probably also in γ-bisabolene14, the ring carbon derived from C-2 of mevalonate isantito the side chain; (4) mevalonolactone andtrans,trans-famesyl pyrophosphate are incorporated into γ-bisabolene without hydrogen loss respectively from C-5 and C-1; cyclisation to the bisabolenyl cation therefore does not involve priortranstocisisomerisation of the terminal double bond of farnesol by a redox mechanism; (5) taken together with our previous findings, it is established thatAndrographiscultures contain two independently functioning enzymes: (i) atrans,trans- tocis,trans-farnesol isomerase, and (ii) atrans,trans-farnesyl pyrophosphate isomerase-cyclase. The absolute configuration of paniculide B has been established by an X-ray cristallographic analysis of its bis-p-bromobenzoate.

ISSN:0008-4042    

DOI:10.1139/v84-355

出版商:NRC Research Press    

年代:1984

数据来源: NRC