Enantioselective Approaches to Aminocyclopentitols: A Total Synthesis of (+)-6-Epitrehazolin and a Formal Total Synthesis of (+)-Trehazolin
摘要:
Potent inhibitors of trehalase, such as trehazolin and its congeners, represent an attractive approach to the design of effective new insect control agents. In this report, enantioselective total syntheses of (-)-6-epitrehazolin and (+)-trehazolin were achieved using the asymmetric heterocycloaddition between [(benzyloxy)methyl]cyclopentadiene and the acylnitroso compound arising from in situ oxidation of (S)-mandelohydroxamic acid with tetrabutylammonium periodate. Further function- alization of the resulting 3,4,5-trisubstituted cyclopentene, either involving osmylation or epoxidation of the double bond, efficiently created pentasubstituted cyclopentanes. Introduction of the quaternary carbon in both synthesis targets was achieved via stereoselective osmylation of an intermediate 2,3,4,5-substituted 1-methylenecyclopentane.
Cyclopentadiene nitroso adducts 1a and ent-1a were synthesised in good yields and good enantiomeric excess from chiral chloro-nitroso derivatives 4 and 5 in the d-mannose and d-ribose series, respectively. The thermal racemisation of these adducts occurred below room temperature. Some other chiral Diels–Alder nitroso adducts were prepared in the d-mandelic, l-prolinol and d-O-methylprolinol series
achiral 1-silyloxybutadiene 1a with the chiral acyinitroso dienophile 2a gave cycloadduct 4 in high diastereomeric excess (d.e. > 98 %), a result which is undoubtedly due to the C-2 symmetrical chiral dimethylpyrrolidine inductor. Excellent d.e. was also observed when the (R)-prolinol dienophile 2d was reacted with the chiral diene 1b (d.e. = 96 %), whereas cycloaddition of the (S) enantiomer 2e with 1b gave
Kirby, Gordon W.; Nazeer, Muhammad, Journal of the Chemical Society. Perkin transactions I, 1993, # 13, p. 1397 - 1402
作者:Kirby, Gordon W.、Nazeer, Muhammad
DOI:——
日期:——
Controlled racemization and asymmetric transformation of α-substituted carboxylic acids in the melt
作者:Eelco J. Ebbers、Gerry J.A. Ariaans、Alle Bruggink、Binne Zwanenburg
DOI:10.1016/s0957-4166(99)00387-0
日期:1999.9
The racemization and asymmetric transformation of a series of cx substituted carboxylic acids, viz. mandelic acid, hydratropic acid, ibuprofen and naproxen, were studied. Several racemization methods for mandelic acid were studied and it was found that base-catalyzed racemization in aprotic polar solvents was the most efficient method. Moreover, a fast and mild base-catalyzed racemization reaction in the melt was developed. DBN turned out to be a very efficient racemizing base for the substrates studied. Combination of the base-catalyzed racemization in the melt with known resolution processes resulted in crystallization-induced asymmetric transformations. Treating racemic ibuprofen or hydratropic acid with 1.5-2.5 equivalents of enantiopure alpha-methylbenzylamine and a catalytic amount of DBN resulted in the isolation of enantiomerically enriched ibuprofen or hydratropic acid with ees of up to 75% and almost quantitative yields. (C) 1999 Elsevier Science Ltd. All rights reserved.
Asymmetric induction in the diels-alder reactions of α-hydroxyacylnitroso compounds
作者:Gordon W. Kirby、Muhammad Nazeer
DOI:10.1016/s0040-4039(00)82298-4
日期:——
Transient, chiral α-hydroxyacylnitroso compounds (2), able to form intramolecular hydrogen bonds, react stereoselectively with cyclopentadiene and cyclohexa-1,3-diene; the cycloadduct (6) of the latter diene and the nitroso derivative of ()-mandelic acid has been converted into the known (-)-oxazine derivative (9).