Abstract: Perhydro-5,5-8a-trimethyl-2-naphthalenone is prepared by acid cyclization of carboxylic esters of formula ##STR1## having a double bond in one of the positions indicated by the dotted lines and wherein symbol R designates a C.sub.1 -C.sub.6 alkyl radical, X stands for a monovalent radical of formula P(O)(OR.sup.1).sub.2 or C(O)R.sup.2, R.sup.1 represents a C.sub.1 -C.sub.6 alkyl group and R.sup.2 is either a linear or branched alkyl group or a substituted or unsubstituted phenyl radical, and wherein the wavy line represents a C--C bond of cis or trans configuration, or of formula ##STR2## wherein the wavy lines and symbol R are defined as above, and R.sup.0 represents a C.sub.3 -C.sub.6 alkyl radical, preferably branched, followed by basic decarboxylation of the obtained product.

Abstract: Perhydro-5,5-8a-trimethyl-2-naphthalenone is prepared by acid cyclization of carboxylic esters of formula ##STR1## having a double bond in one of the positions indicated by the dotted lines and wherein symbol R designates a C.sub.1 -C.sub.6 alkyl radical, X stands for a monovalent radical of formula P(O)(OR.sup.1).sub.2 or C(O)R.sup.2, R.sup.1 represents a C.sub.1 -C.sub.6 alkyl group and R.sup.2 is either a linear or branched alkyl group or a substituted or unsubstituted phenyl radical, and wherein the wavy line represents a C--C bond of cis or trans configuration, or of formula ##STR2## wherein the wavy lines and symbol R are defined as above, and R.sup.0 represents a C.sub.3 -C.sub.6 alkyl radical, preferably branched, followed by basic decarboxylation of the obtained product.

Abstract: The cycloaliphatic aldehydes of formula ##STR1## wherein R.sup.0, R.sup.1 and R.sup.2 represent independently a hydrogen atom or a lower alkyl from C.sub.1 to C.sub.6 and X stands for a group of formula ##STR2## wherein R.sup.3 and R.sup.4 represent independenly a lower alkyl radical from C.sub.1 to C.sub.3 and R.sup.5 represents a lower alkyl radical or hydrogen, provided that R.sup.1, R.sup.3 and R.sup.4 do not represent simulataneously a methyl radical whenever R.sup.0 and R.sup.2 represent each a hydrogen atom, are prepared from enol esters of formula ##STR3## wherein the wavy line stands for a --C--O-- bond of cis or trans configuration, Y represents an acyl group or P(O)(OR).sub.2, wherein R stands for a lower alkyl monovalent radical or an aryl, and Z defines a group of formula ##STR4## wherein R.sup.3, R.sup.4 and R.sup.5 are defined as above, by cyclisation carried out by means of an acidic cyclisation agent.

Abstract: Racemic and optically active cycloaliphatic 2,2,6-trimethylcyclohexanecarboxyaldehyde, also known as dihydrocyclocitral, are prepared by a novel process consisting in the cyclization of enol esters of formula ##STR1## wherein the wavy line defines a C--O bond of cis or trans configuration, X represents an acyl group or P(O)(OR).sub.2, wherein R stands for a lower alkyl monovalent radical or an aryl, and Z represents a monovalent radical of formula ##STR2## by means of an acid cyclization agent.

Abstract: Racemic and optically active cycloaliphatic 2,2,6-trimethyl-cyclohexanecarboxaldehydes, also known as dihydrocyclocitral, are prepared by a novel process consisting in the cyclization of enol esters of formula ##STR1## wherein the wavy line defines a C--O bond of cis or trans configuration, X represents an acyl group or P(O)(OR).sub.2, wherein R stands for a lower alkyl monovalent radical or an aryl, and Z represents a monovalent radical of formula ##STR2## by means of an acid cyclization agent.