Acetals 2-iodo, from enol acetates

HI hi acetic acid allows the reduction of jS-peracetates of the higher sugar N-acetylneuraminic acid to the corresponding anomeric deoxy compounds.277 At room temperature this method gave exclusively the a-anomer, whereas at —20 °C a 4 1 a [i ratio resulted. This may be explained by thermodynamic and kinetic protonation of ester enolates generated in situ from anomeric iodide in a manner reminiscent of previous reductions of 2-iodo sugar lactones.278... 

As a sequel to the elegant and highly efficient synthesis of camphor by an intramolecular cyclization. Money et have successfully applied this method to the synthesis of the naturally-occurring sesquiterpenoids campherenone (110) and campherenol (111) whose structures and absolute stereochemistries have recently been deduced.In this sequence, dihydrocarvone (112) was readily converted into the keto-ketal (113) from which the homologated chloro-ketone (114) was obtained. Treatment of the corresponding enol acetate (115) with boron trifluoride in wet methylene chloride afforded the two bicyclic chloro-ketones (116) and (117) in 55-60% yield. Conversion of the corresponding iodo-ketals... 

The dihydroxy-ketal (240), previously prepared from ( —)-santonin, has been used to synthesize a number of related sesquiterpenoids. Thus the diacetate of (240) was converted in six steps into (241), which was then treated with iso-propenyl acetate-sulphuric acid the derived enol-acetate was cleaved to the triol (242) by ozonolysis and lithium aluminium hydride reduction. The triol (242) was then converted into the di-iodo acetate (243) in a number of steps and thence to shyobunone (244) by dehydroiodination, reduction, and oxidation. Thermolysis of shyobunone at 160—180 °C gave preisocalamendiol (245) in about 30% yield. More recently, Iguchi et al. have shown that preisocalamendiol (245) can be cyclized to isocalamendiol (246) in aqueous acetic acid no trace of calamendiol (247) was found. A number of other interesting acid-catalysed cyclizations have been observed in this area, e.g. the formation of (248 R = OH) and (248 R = OAc) from (249) and the formation of (250) from (251). Finally, e-cadinene (252) has been obtained from (253), the lithium aluminium hydride product of preisocalamendiol (245). 

The SrjjI reaction of o-iodo and o-bromo-benzoate salts with CHjCOMe ion affords the substitution product ca. 78% yield), which upon acid treatment with toluene p-sulphonic acid gives the corresponding isocoumarin 15 (90%) (Scheme 4). Benzazepines 16 can be produced upon ammonium acetate treatment of the substitution compound obtained in the reaction of (o-iodophenyl) acetic acid derivatives with enolate ions from ketones ( CHjCOR, R = Me, i-Pr, t-Bu 50, 60, and 56%, respectively) (Scheme 5)." ... 

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