= Solution
An <acetal> <retrosynthesis> separates the target into \b[trans-cyclohexane-1,2-diol and cyclohexyl methyl <ketone>]. Both fragments can be prepared using separate portions of <cyclohexene>.
For the diol, <epoxidation> with a <peroxy acid> such as mCPBA gives <cyclohexene> oxide. Acid-catalysed opening with water occurs by backside attack on the protonated <epoxide>, giving the \b[anti, hence trans, diol]. A syn dihydroxylation would give the wrong relative configuration.
For the <ketone>, add HBr to another portion of <cyclohexene> to obtain bromocyclohexane, form its <grignard reagent> with Mg in dry ether, and add <acetonitrile>. Hydrolyse the resulting <magnesium> imine salt to $\mathrm{C_6H_{11}COMe}$. A <nitrile> is useful here because addition followed by <hydrolysis> stops at the <ketone> instead of giving the double addition associated with an <ester>.
Finally combine the isolated trans diol and <ketone> with catalytic acid and remove water to form the cyclic <ketal>. The <ketone> <carbon> becomes the <acetal> <carbon> bearing Me and cyclohexyl; the two original diol C–O bonds retain their relative configuration. \b[Anti <epoxide> opening supplies the required trans relationship before <ketal> formation.] <ketal> formation is an equilibrium and the trans-fused product may be less favourable than an unstrained <acetal>, so effective water removal and isolation are necessary; substituting a cis diol is not an acceptable shortcut.
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