Photoannulation and ring closing metathesis of carbohydrate derivatives

2014-12-15T10:35:45Z (GMT) by William D. Barker
The 'chiron approach' is a well-recognised technique for converting carbohydrates and other naturally occurring compounds into new chiral target molecules. The success of this area of chemistry can be attributed to the vast array of novel methods for transforming carbohydrates that have been developed over the last 50 years. Chapter 1 describes some of the key discoveries and pioneers within the field of carbohydrate annulation.;As part of the Jenkins groups' on-going studies into the development of new methods for carbohydrate annulation, we have demonstrated the ease in which simple carbohydrate derivatives can be cyclised by Ring Closing Metathesis (RCM). Using Grubbs ruthenium catalyst 176b, we have cyclised a range of substrates derived from D-glucose to give annulated products such as 307. Some of the adducts have been reduced by well known methodology to give chiral fragments such as 348 which may be used as 'chiron' in further synthesis (Chapter 2). (Fig. 10916A).;We have also utilised the copper (I) triflate catalysed intramolecular [2+2] photocycloaddition reaction to cyclise a range of carbohydrate derivatives such as 306 to afford enantiomerically pure products 400 and this represents a novel method to add to the increasingly wide range of techniques for annulating carbohydrates. (Fig. 10916B).;To further extend the scope of the catalysed [2+2] photochemical ring closure reaction, we have investigated a variety of reagents in an attempt to make it an asymmetric catalytic process. The chiral diene 535 can be cyclised in the presence of a number of chiral catalysts such as 554 to give two enantiomeric tricyclic products 536a and 536b, which can be quantitatively analysed by chiral hplc. The chiral catalyst should favour on enantiomer over the other. We have considered a variety of substrates, reagents and reaction conditions, and the results are reported in chapter 4. (Fig. 10916C).




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