Beilstein J. Org. Chem.2014,10, 2200–2205, doi:10.3762/bjoc.10.227
yields (66–95%) and without the need for chromatographic purification.
Keywords: azabicycloalkene; β-hydroxyketone; 2-isoxazoline; oxabicycloalkene; Raney nickel; Introduction
2-Isoxazolines 1 are practical precursors to countless structural motifs found in nature. Various carbonyl compounds 2, β
Beilstein J. Org. Chem.2007,3, No. 48, doi:10.1186/1860-5397-3-48
following two reasons: 1. Azabicycloalkene 7 is easy to synthesize via Diels-Alder reaction.[62] 2. It was assumed to be a good substrate for RORCM because it is strained and has been shown to be susceptible to other desymmetrizing ring opening reactions in the past.[63][64]
To generate appropriate
isoindole derivative 11 in good yield, verifying our previous assumptions.
As a general trend, it turned out that benzannelated azabicycloalkene derivatives like 8 and 10 give relatively unstable products. In consequence, products can only be isolated as pyridones 9, derived from spontaneous aromatization
desymmetrization of bis-olefin 10 with the known chiral ruthenium catalyst 3.[67] This reaction gave enantioenriched 11 in good yield (Scheme 5). However, the enantioselectivity of this reaction is only moderate compared to similar reactions using molybdenum based precatalysts and different azabicycloalkene
PDF
Graphical Abstract
Figure 1:
Ruthenium based precatalysts used in this study.