Sugars cyclohexylidene deriv

Cyclohexylidene derivatives of 1,2-diob. Whereas 1,2-diols had traditionally been characterized by reaction with acetone to produce the acetonide or isopropylidene derivatives, Micovic and Stojiljkovic recommended conversion of sugars and other polyols into their cyclohexylidene derivatives because of the ease with which these substances crystallize. Angyal et al. explored the behavior of inositol (1) and found that this cyclitol gradually dissolved in a mixture of cyclohexanone and benzene containing p-toluenesulfonic acid on boiling under a Dean-Stark water separator. 

In continuation of their studies of the resolution of myo-inositol derivatives via their orthoesters with sugar derivatives, Evstigneeva et al. [296] converted the racemic 1,2 3,4-di-O-cyclohexylidene-wyo-inositol (431) by transesterification with the mannose orthoester (425) into a mixture of diastereoisomers (426) formed by esterification of the 5- and 6-positions of (431). One of the four possible isomers was separated by crystallisation and the other three were obtained by preparative TLC. Partial hydrolysis of the resolved isomers gave both enantiomers of 1,2-0-cyclohexylidene-myo-inositol (432). 

It was found that die stereoselectivity of reduction was increased by ethanol, and that (R)-l-phenylethanol was obtained in 70% optical yield when acetophenone (12.5 mmoles) was reduced with an ethanol-modified complex of lithium aluminum hydride with 3-O-benzyl-1,2-O-cyclohexylidene-a-D-glucofuranose prepared from the sugar derivative (26 mmoles), lithium aluminum hydride (58 mmoles), and ethanol (110 mmoles). 

Diethyl azodicarboxylate and triphenylphosphine permit the condensation between aldose derivatives with a free reducing centre and phenols. 2,3 5,6-Di-0-isopropylidene-D-mannose gave 67% of the phenyl o-D-mannofuranoside derivative and 16% of the /3-anomer, while 2,3 4,6-di-O-cyclohexylidene-a-D-mannose afforded access to p-nitrophenyl /3-D-mannopyranoside in 58% yield and other, substituted aryl analogues. Unsubstituted sugars can be subjected to the procedure, D-glucose giving mainly the phenyl 3-pyranoside. ... 

Free Sugars and Simple Derivatives Thereof. — Partially deuteriated j8-L-arabino-pyranose and a-L-xylopyranose (n.d. refinement), 1,2-6>-cyclohexylidene- and l,2-O-isopropylidene-0 -D-glucofuranose 3,5,6-phosphites, 5-O-acetyl-l,2 3,4-di-O-isopropylidene-a-D-galactoseptanose, 3,4,6-tri-O-acetyl-l, 2-0-(R )-ethyl-... 

The n.m.r. spectroscopic investigation of the reactions of pentonolactones with acetone and benzaldehyde in acidic media is covered in Chapter 21, as are conformational studies on 2,3-G-isopropylidene-a-L-sorbopyranose derivatives. l,2-0-Isopropylidene-a-D-t /o-pentodialdo-l,4-furanose dimers are referred to in Ch er 22, and some 7-carbon sugar lactones which were characterized as their isopropylidene-and cyclohexylidene-acetals are noted in Chtytters 2 and 16. 

The stereochemistry of the products of nucleophilic addition of phenylacetic acid dianion to l,2 5,6-di-Q-cyclohexylidene-a-D-ti -hexofuranos-3-ulose has been determined - partly by use of circular dichroism. Base treatment of the Q-mesylcyanohydrin (1) of the furanos-3-ulose (2) afforded spiro-oxathiole-2,2-dioxide (3) which cleaved with methoxide anion to give the branched-chain sugar derivative (4) (Scheme 1). Similar results were obtained... 

A number of synthesis of amino-sugars from chiral non-carbohydrate starting materials have been reported. A reaction sequence used previously to synthesize 2-amino-2-deoxy-D-ribose from 2,3-0-isopropylidene-D-glyceraldehyde (V0I.I6, p.92-3) has been improved K) achieve better stereoselectivity in the initial aldol condensation used to extend the chain by two carbon atoms. The synthesis of a 6,6,6-trifluoro-L-daunosamine derivative from 2,3-0-cyclohexylidene-D-glyceraldehyde is covered in Chapter 8, and of 2,5-dideoxy-2,5-imino-pentonic acids from tartaric acid in Chapter 16. 

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