Forming five membered nngs

Furanose form (Section 25 6) Five membered nng ansing via cyclic hemiacetal formation between the carbonyl group and a hydroxyl group of a carbohydrate... 

Cycloadditions. 1,3 Dipolar cycloadditions certainly have been the most important means of forming fluorinated five-membered rings Ruonnated substances, however, have also been used in other classic five-membered-nng-... 

Five-membered nng systems are also formed on transfer of single-skeletona-tom fragments, usually in a stepwise process CR2 from diazo alkanes [261J, NH from azounide (hydrazoic acid) [134], O from peroxy acids [/5J], S from phos-... 

Aldoses incorporate two functional groups C=0 and OH which are capable of react mg with each other We saw m Section 17 8 that nucleophilic addition of an alcohol function to a carbonyl group gives a hemiacetal When the hydroxyl and carbonyl groups are part of the same molecule a cyclic hemiacetal results as illustrated m Figure 25 3 Cyclic hemiacetal formation is most common when the ring that results is five or SIX membered Five membered cyclic hemiacetals of carbohydrates are called furanose forms SIX membered ones are called pyranose forms The nng carbon that is derived... 

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