Tetrahydropyrans synthesis acetylation

Acetate pyrolysis is illustrated by the synthesis of penta-1,4-diene (Expt 5.14) from 1,5-diacetoxypentane. This is prepared from 5-chloropentyl acetate which is conveniently obtained from tetrahydropyran by treatment with acetyl chloride this ring-opening reaction offers interesting comparison with the methods for the preparation of a, cu-dihalides discussed in Section 5.5.1, p. 555. 

Among tetrahydropyran anhydrosugar derivatives the most common are 3,6-anhydro-pyra-noses. An example illustrating the synthesis of such types of compounds is the preparation of methyl 3,6-anhydro- -D-glucoside from methyl 2,3,4-tri-0-acetyl-6-bromo-6-deoxy-/3-D-gluco-pyranoside upon treatment with barium hydroxide. 3,6-Ahydro-D-galactose and 3,6-ahydro-D-mannose are prepared in a similar way (O Fig. 20). 

The aldehyde 218 possessing 2,6-frans-tetrahydropyran, was synthesized as shown in Scheme 48. /3-Keto ester 220 was reduced by Noyori hydrogenation [97] to give 6-hydroxy ester 221 in 94% ee, which was converted into iodide 222. Asymmetric alkylation using Myers chiral auxiliary [98] with 222, followed by acid treatment, furnished 5-lactone 223 with high stereoselectivity. Reductive acetylation, axial allylation by the Hosomi-Sakurai reaction, and ozonolysis completed the synthesis of 218. 

Last year saw the application of D-xylose to the synthesis of sesbanimide and this strategy has been extended to encompass ring C variants. A new synthesis of the cosmetic component 70 (a well-studied synthetic target that is derived from the civit cat) from 3,4-di-O-acetyl-L-rhamnal has been developed and the same group have described the use of L-rhamnal for synthesis of L-oleandrose 71. Methyl 6-deoxy-2,3-0-isopropylidene-a—D-mannopyranoside provides a flexible precursor to a series of deoxysugars (tetrahydropyrans), a-D-amicetoside 72, a-D-perosaminoside 73 and a-D-janoside 74.49... 

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