Cyclogeranate

Cyclogeranic acid, 24 570 Cycloheptaamylose, 4 714 Cycloheptylamine, physical properties of, 2 498t... 

Methyl alcohol. See Methanol Methyl a-cyclogeranate, 24 569 Methyl a-hydroxyisobutyrate, 16 247 Methyl allyl carbonate, molecular formula, 6 305t... 

One synthetic route to the damascones starts with an appropriate cyclogeranic acid derivative (halide, ester, etc.). This is reacted with an allyl magnesium halide to give 2,6,6-trimethylcyclohexenyl diallyl carbinol, which on pyrolysis yields the desired l-(2,6,6-trimethylcyclohexenyl)-3-buten-l-one. Damascone is obtained by rearrangement of the double bond in the side-chain [98]. 

Thermal decomposition of the oligomeric ester produced a- and /3-cyclogeranic acids in 47% and 30% yields, respectively. Other preparative methods for these acids is described (1). 

Methyl P-safranate (700) is readily prepared from methyl p-cyclogeranate (701), by epoxidation and opening of the epoxide with Filtrol . If there is no activa-... 

We have mentioned the ozonolysis of p-ionone leading to P-cyclocitral (Vol. 4, p. 531, Ref. 550). The principle has now been extended to the epoxide (708) of a-ionone, and from the epoxides obtained [those of a-cyclocitral (709, R = CHO) or methyl a-cyclogeranate (709, R = COOMe)], the hydroxylated compounds 710 (R = CHO) and710(R = COOMe) have been prepared. 

The damascones are a group of materials related to the ionones, but in which the enone unit is transposed. They are components of rose oils and have very intense fruity-floral odours. The damascenones, which contain a second double bond in the ring, are also very much sought after. One synthesis of a-damascone from methyl a-cyclogeranate is shown in Scheme 4.40. A double Grignard addition gives the tertiary alcohol. Heating of this in the presence of base, to prevent elimination... 

Cyclohexene-1-carboxylic acid, 2,6,6-trimethyl- cyclogeranic acid)... 

A -Cyclogeranic Acid ( -Cyclogeranic acid, 1 3 Z-irimdhylcyclohexene-2-oarboxylic acid)... 

A -Cydogeranic Acid (a-Cyclogeranic acid, 1.-5 54rimeBiylcyclohexene-6.carboxylic add)... 

Scheme 1-7. Deracemization of methyl a-cyclogeranate (11) and a-damascone (12) by enolate protonation with (+)- and (-)-Y-isopropylephedrine.

In the course of such investigations, an extremely simple way for the transformation of methyl P-cyclogeranate into its nonconjugated and hence energetically less favorable y-isomer was found (Scheme 1-8). The desired ester (70%) is obtained without any isomeric contamination as a racemate when the LlDA-produced enolate 13a [M = Li] is trapped with chlorotrimethylsilane and the resulting mixed ketene acetal 13b [M = Si(CH3)3] is subsequently hydrolyzed. 

Scheme 1-8. "Up-hill" isomerization of methyl P-cyclogeranate into the y-isomer through the lithium enolate 13a and the (7-silyl enether 13b.

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