256
S. Breitenlechner, P. Selig, T. Bach
ples of its use are discussed in this report. It was shown that the general working
mode of such a template can also be applied to radical reactions, irrespective
of whether the radical chain process is initiated photolytically or chemically.
While the robustness of template 12 allows for its almost quantitative recovery
and its reuse, it has so far been used in a catalytic sense only in a single case. For
the development of photochemical organocatalysts it was proposed to prepare
modified templates, in which a light-collecting device acts simultaneously as
sensitiser and as a steric shield. A prototype 40 for such a template was devised
and it was shown that it can indeed induce catalytic turnover in a photoinduced
electron transfer reaction.
1
Introduction
The synthesis of chiral compounds in enantiomerically pure form is one
of the most important and one of the most challenging goals of modern
organic synthesis. Any key step of synthetic importance, which leads to
the creation of a stereogenic centre, requires to be studied with regard
to its stereoselectivity. Impressive progress has been made along these
lines in the last decades. The number of catalytic enantioselective reactions increases continuously (Ojima 2000; Berkessel and Gröger 2005).
In our group, organic photochemistry has been used frequently for
the synthesis of chiral natural products and other biologically active
compounds. A typical example is the synthesis of (+)-preussin (Basler
et al. 2005), the photochemical key step of which is depicted below
(Scheme 1). Starting from L-pyroglutamic acid (1), dihydropyrrole 2
was synthesised in eight steps, the attachment of the alkyl side chain by
nucleophilic substitution with a cuprate being the decisive C–C bond
formation. The subsequent photocycloaddition served to introduce the
stereogenic centers at C-2 and C-3 in a diastereoselective fashion (Bach
and Brummerhop 1998; Bach et al. 2000a). Oxetane 3 was hydrogenolytically cleaved and subsequently the N-methoxycarbonyl group was
reduced to produce the desired target, (+)-preussin (4), which was later
shown to act as cyclin-dependent kinase inhibitor (Achenbach et al.
2000).
S. Breitenlechner, P. Selig, T. Bach
ples of its use are discussed in this report. It was shown that the general working
mode of such a template can also be applied to radical reactions, irrespective
of whether the radical chain process is initiated photolytically or chemically.
While the robustness of template 12 allows for its almost quantitative recovery
and its reuse, it has so far been used in a catalytic sense only in a single case. For
the development of photochemical organocatalysts it was proposed to prepare
modified templates, in which a light-collecting device acts simultaneously as
sensitiser and as a steric shield. A prototype 40 for such a template was devised
and it was shown that it can indeed induce catalytic turnover in a photoinduced
electron transfer reaction.
1
Introduction
The synthesis of chiral compounds in enantiomerically pure form is one
of the most important and one of the most challenging goals of modern
organic synthesis. Any key step of synthetic importance, which leads to
the creation of a stereogenic centre, requires to be studied with regard
to its stereoselectivity. Impressive progress has been made along these
lines in the last decades. The number of catalytic enantioselective reactions increases continuously (Ojima 2000; Berkessel and Gröger 2005).
In our group, organic photochemistry has been used frequently for
the synthesis of chiral natural products and other biologically active
compounds. A typical example is the synthesis of (+)-preussin (Basler
et al. 2005), the photochemical key step of which is depicted below
(Scheme 1). Starting from L-pyroglutamic acid (1), dihydropyrrole 2
was synthesised in eight steps, the attachment of the alkyl side chain by
nucleophilic substitution with a cuprate being the decisive C–C bond
formation. The subsequent photocycloaddition served to introduce the
stereogenic centers at C-2 and C-3 in a diastereoselective fashion (Bach
and Brummerhop 1998; Bach et al. 2000a). Oxetane 3 was hydrogenolytically cleaved and subsequently the N-methoxycarbonyl group was
reduced to produce the desired target, (+)-preussin (4), which was later
shown to act as cyclin-dependent kinase inhibitor (Achenbach et al.
2000).