Preisocalamendiol

In order to explain the stereospecificity of the thermally induced cyclization of preisocalamendiol (315) to give dehydroisocalamendiol (316), Terada and Yamamura have carried out molecular mechanics calculations on the ground-state conformers and probable transition states of (315). The computed values of the steric energies of the possible transition states are in good agreement with the observed experimental facts. Other studies related to the conformational aspects of germacrane sesquiterpenoids include an examination of the NOE effects in the isofuranodiene (317), which shows the 1,5-diene system to be in a crossed... 

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). 

Production By steam distillation from the roots of calamus (Acorus calamus), origin eastern Europe. CompositionC. consists mostly of sesquiterpenoid compounds. Typical components are shyobunone (C15H24O, Mr 220.35) and its isomers (together ca. 8-10%), as well as preisocalamendiol (C15H24O, Mr 220.35) (8%) and acorenone (C,5H240, Mr 220.35) (11 %). The characteristic component of calamus is cis-asarone ()3-asarone, see asarones) present to about... 

Piperinic acid, T1 Piperitenone oxide, T4 Piperitols, T4 Piperitone, T2 Piperitone oxide, T4 Pipitzols, T1 Pisatin, Y3 Piscidic acid, A30 Plathyterpol, T39 Platicodigenin, T45 Platydesmine, K31 Platynecine, K22 Plicatic acid, Y7 Plinols, T3 Plumericin, T16 Plumieride, T16 Pluviine, K6 Podocarpic acid, T33 Podolactones, T38 Polyether antibiotics, Yll Polyporenic acid A, T50 Ponasterone, T48 Porantherine, K29 Porphyrins, Y23 Portentol, Y15 Portulal T40 Preisocalamendiol, T22 Pretoxin, T31 Pristimerin, T45 Pristimerol, T45 Proaporphine alkaloids, K3 Proline, All Prolinol, A17 Pronuciferine, K3 19-propylthevinol, K4 Prostaglandins, Y16 Protoaphins, YIO Protoemetine, K2 Protostanes, T50... 

Iguchi M, Nishiyama A 1970 Preisocalamendiol, a plausible precursor of isocalamendiol. Tetrahedron Lett 855-857... 

Porantheridine, K7 Porantherine, K29 Porphyrins, Y23 Portentol, Y15 Portulal, T40 Practolol, All Prehelminthosporol, K9 Preisocalamendiol, T22 Prenylamine, A17 Prenylsolanone, TIO Presqualene alcohol, T14 Pretoxin, T31 Prezizaene, T29 Pristimerin, T45 Pristimerol, T45 Proaporphine alkaloids, K3 a-prodine, A18 ... 

The homoallylic alcohol (90) is cyclized to s-cadinene (91) by reaction with methanesulfonyl chloride in pyridine 145). An intramolecular Prins reaction of the corresponding ketone (preisocalamendiol, 92) is effected by treatment with aqueous acetic acid, giving isocalamen-diol (93) 146). 

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