(12) A. B. Bahadoor, G. C. Micalizio “Studies in Macrolide Antibiotic Synthesis: The Role of Tethered Alkoxides in Titanium Alkoxide-mediated Regioselective Reductive Coupling Reactions”
Finally, we examined the behaviour of alcohol 12 under cross-metathesis conditions. In the event, two isomerised products were isolated from this reaction (Scheme ): the internal alkene 16 (formed in 99% yield as a ca. 3:1 mixture of E:Z isomers) and the acylsilane 17. The formation of isomerised alkenes accompanying (or instead of) metathesis processes using ruthenium-based catalysts is well documented, [-] as is the formation of carbonyl compounds by isomerisation of the corresponding allylic alcohols. [-] At this stage we therefore reluctantly abandoned our investigations into the asymmetric synthesis of tashiromine.
A Novel Synthesis of Functionalized Allylsilanes - …
In Situ Generation of Phosphoryl Alkylindiums and Their Synthetic Application to Arylalkyl Phosphonates via Palladium-Catalyzed Cross-Coupling Reactions2014,
Allylsilanes have been used extensively over the last 30 years
The use of the allyltrimethylsilane cross-metathesis approach enables the rapid construction of the key cyclisation precursor 3 (3 steps from commercial materials), which undergoes acid-induced cyclisation to give the desired bicyclic indolizidine skeleton as a 96:4 mixture of diastereomers. Simple functional group interconversions allowed the completion of the total synthesis of racemic tashiromine in six steps (19% overall yield). Three chiral α-alkoxyallylsilanes (12,14 and 15) were prepared in enantioenriched form and their cross-metathesis reactions studied as part of a putative asymmetric approach to tashiromine. In the event, α-hydroxysilane 12 underwent isomerisation under the reaction conditions to acylsilane 17, while silanes 14 and 15 were unreactive towards metathesis.
Carbon chain synthesis by allylic substitution, allylation
Alkenylation of Phosphacoumarins via Aerobic Oxidative Heck Reactions and Their Synthetic Application to Fluorescent Benzophosphacoumarins 2015,
The Chemical Record 2016 , 16 , 124
Tashiromine 1 is a naturally occurring indolizidine alkaloid. It has been the subject of thirteen successful total syntheses to date. Our own approach centres on the stereoselective construction of the indolizidine core by capture of an electrophilic acyliminium species by a pendant allylsilane. The key cyclisation precursor is constructed using olefin cross-metathesis chemistry, which has the potential to facilitate both racemic and asymmetric approaches, depending upon the choice of the allylsilane metathesis partner.
General & Introductory Chemistry
Synthesis of Azepinoindoles via Rhodium-Catalyzed Formal Aza-[4 + 3] Cycloaddition Reaction of 3-Diazoindolin-2-imines with 1,3-Dienes in One-Pot 2017,