NOVELTY - Preparing (P1) substituted 4',9'-dihydro-3'H-spiro(cyclohexane-1,1'-pyrano(3,4-b)indole) compound (I), or its acid addition salt, involves: (a) reacting 2-(5-fluoro-1H-indol-3-yl)-ethanol with a substituted methyl-(1-phenyl-cyclohexyl)-amine compound, in each case optionally in the form of an acid addition salt, in the presence of at least one mono- or diprotic acid promoting agent, in a carbonic acid reaction medium (A1) to form the compound (I).    USE - For preparing substituted 4',9'-dihydro-3'H-spiro(cyclohexane-1,1'-pyrano(3,4-b)indole) compound or its acid addition salt (claimed) useful as analgesic.    ADVANTAGE - The process has advantages over conventional processes for the preparation of the compound (I), in particular with respect to influencing the stereoselectivity such as the diastereoselectivity of the process in a targeted manner and at least partially suppressing the formation of undesired side-products and/or undesired diastereomers, and further with respect to employing environmentally acceptable conditions especially in view of a large-scale synthesis of ((1R,4R)-1) and ((1R,4R)-2) in multigram quantities; and is more cost-efficient process. The process allows for the preparation of compound (I) in pure diastereomeric forms in at least one carbonic acid such as acetic acid as reaction medium, i.e. allows for employing environmentally acceptable conditions especially in view of a large-scale synthesis of compound (I) in multigram quantities; and allows for sparing the use of solvents such as halogenated solvents e.g. dichloromethane, which are assessed to be at least environmentally critical. In addition, the size of the required reactor can be reduced significantly due to the lower dilution making the process more cost-efficient.    DETAILED DESCRIPTION - Preparing (P1) substituted 4',9'-dihydro-3'H-spiro(cyclohexane-1,1'-pyrano(3,4-b)indole) compound of formula (I), or its acid addition salt, involves: (a) reacting 2-(5-fluoro-1H-indol-3-yl)-ethanol with a substituted methyl-(1-phenyl-cyclohexyl)-amine compound of formula (II), in each case optionally in the form of an acid addition salt, in the presence of at least one mono- or diprotic acid promoting agent, in a carbonic acid reaction medium (A1) to form the compound (I).    R1=H or CH3;or    R2+R3==O;or    CR2R3=cyclic groups of formulae (i) or (ii);    R4 and R5=0-4 substituents selected from H and CH3.    An INDEPENDENT CLAIM is included for a the compound (I) (where R1 is CH3) or its acid addition salt produced by the process (P1).