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Synthesis 2001(15): 2341-2347
DOI: 10.1055/s-2001-18432
SPECIALTOPIC
© Georg Thieme Verlag Stuttgart · New York

New Methods for the Synthesis of P-Chirogenic Diphosphines: An Application to the Development of an Improved Asymmetric Variation of the Rh(I)-Catalyzed [4+2] Cycloaddition

Holly Heath, Bradley Wolfe, Tom Livinghouse*, Sun Kun Bae
Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA
e-Mail: livinghouse@chemistry.montana.edu;
Further Information

Publication History

Received 31 July 2001
Publication Date:
05 August 2004 (online)

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Abstract

A series of new P-chirogenic diphosphines has been prepared by efficient and complementary synthetic procedures. The utilization of a series of these bidentate ligands possessing steric linker variations and a conserved P-chirogenic domain in an asymmetric variation of the Rh(I)-catalyzed [4 + 2] enediene cycloaddition is described.

Key words

P-chirogenic ligands - dynamic resolution - catalysis - cycloadditions

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6

The use of this substrate gave exceptionally well resolved HPLC traces so that optimization of the conditions for dynamic resolution could be readily achieved.

7

In all instances involving monohalide trapping agents, an authentic sample of racemic phosphine-borane was prepared for comparison by chiral HPLC.

9

Reprotection of the diphosphines derived from 4b, 6c, 6d and 6e with BH3·THF and analysis by HPLC (CHIRALPAK AD) established that no epimerization occurs during the pyrrolidine mediated deprotection reaction.

13

In general, recrystallization to near optical purity could most readily be achieved by solvent diffusion in a closed system.

14

In the case of 9b, separation of the isomers 10b in an authentic racemic mixture by chiral HPLC was not achieved. For this reason, optical purity was established for the corresponding P-benzyl derivative.