Stereocontrolled synthesis emerged from chemists' need to create organic molecules with precise three-dimensional arrangements. In the context of alkene preparation, it is desirable to control the configuration of the newly formed C-C double bonds, as the E-and Z-alkene isomers often manipg. 1 of 19 fest distinct properties. Interestingly, not only simple physicochemical properties such as melting or boiling temperature, but also biological function of E and Z-isomers can be very different. One of such examples are fatty acids, where Z-configured ones are vital components of edible plant oils, while E-fatty acids are believed to contribute to obesity, cardiovascular diseases, and diabetes. Similarly, E/Z-geometric isomers of insect sex pheromones have often different effects on mating behaviour. Different olfactory sensation of E and Z-geometric isomers are also well documented, and often one isomer has distinctly more enjoyable (to humans) scent than the other. In this context, it is considered that in many cases Z-isomers have a more pleasant smell and are more "natural" than E-ones. For instance, (Z)-hept-4-enal isomer possesses a pleasant cream-buttery scent, whereas the E-isomer is known for its pungent putty-like odour. Similarly, Z-configured macrocyclic musk are considered as one of the most valued in the flavour and fragrance industry. These compounds can be acquired from animals (e.g. civetone from Civettictis civetta, African civet) or synthesised. In the latter case, catalytic olefin metathesis can be considered as one of the favourite methods to produce unsaturated musk via ring-closing metathesis macrocyclisation (mRCM). Unfortunately, preparation of medium and large rings by RCM of unbiased dienes was usually conducted under the so-called high dilution conditions (1-10 mM), making mRCM impractical from the industrial perspective due to high costs of utilising and disposing of very large volumes of organic solvents needed in the synthesis. Recently, using a polymerisation-depolymerisation metathesis reaction under reactive distillation conditions, we pioneered with an efficient mRCM technique producing a number of unsaturated musk as mixtures of E and Z-isomers at concentration of 200-700 mM.