= Solution
Disconnect the N–cyclohexyl bond as a late <reductive amination> of a primary amine with <cyclohexanone>. Disconnect the exocyclic methylene as a <Wittig methylenation> of a substituted <cyclohexanone>. The useful ring precursor is \b[3-methyl-5-substituted cyclohex-2-en-1-one], accessible by a <Robinson annulation>. The pendant substituent throughout ring construction should be $(\mathrm{CH_2})_4\mathrm{NHBoc}$.
Start with <nucleophilic substitution> of the supplied bromo <ester> by cyanide:
$$
\mathrm{Br(CH_2)_3CO_2Me}
\longrightarrow\mathrm{NC(CH_2)_3CO_2Me}.
$$
Reduce the <nitrile> selectively to the primary amine while retaining the <ester>, for example by controlled catalytic <hydrogenation> with <Raney nickel> in the presence of ammonia, and trap the amine promptly as its Boc <carbamate>. Avoid heating or concentrating the free amino <ester>, which can cyclize to a <lactam>. <lithium aluminium hydride> would be unsuitable at this stage because it also reduces the <ester>.
Partial reduction of the protected <ester> with DIBAL at low temperature gives $\mathrm{BocNH(CH_2)_4CHO}$. The <carbon> of the original <nitrile> is now the methylene nearest <nitrogen>; the original <ester> <carbonyl> is the <aldehyde> <carbon>. Condense this <aldehyde> with <acetone> and dehydrate to $\mathrm{BocNH(CH_2)_4CH{=}CHCOMe}$.
Now add the <enolate> of a second <acetone> molecule in a <Michael addition>. With $R=(\mathrm{CH_2})_4\mathrm{NHBoc}$, the resulting chain is
$$
\mathrm{MeCOCH_2CH(R)CH_2COMe}.
$$
Intramolecular <aldol condensation> gives \b[3-Me-5-R-cyclohex-2-en-1-one]. The beta methyl derives from the <carbonyl> end attacked in the ring closure; the pendant aminoalkyl chain remains at C5. Hydrogenate the ring C=C selectively, retaining the <ketone>, then methylenate the <ketone> with preformed $\mathrm{Ph_3P{=}CH_2}$. Do the <hydrogenation> before installing the exocyclic methylene so that it is not hydrogenated away.
Remove Boc under brief mild conditions, checking for acid-induced exocyclic <alkene> isomerization. <reductive amination> of the resulting primary amine with <cyclohexanone>, followed by selective imine reduction, installs the secondary N-cyclohexyl group. Use controlled stoichiometry to suppress tertiary amine formation. \b[The methyl and four-carbon aminoalkyl substituents occupy the required 1,3-related ring positions, with the exocyclic methylene at the former <carbonyl>.] No ring <stereochemistry> is specified. The target contains eighteen <carbons>: six ring <carbons>, one ring methyl, one methylene, four in the linker, and six in the N-cyclohexyl group.
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