The synthesis of 3-methyl-1,4-dioxacylopentadecan-2-one (12c) and 3-methyl-1,4-dioxacylohexadecan-2-one (12d), two new musk odorants, is described starting from methyl 2-bromopropionic acid (6b) and allylic alcohol, respectively. The key step of the synthesis is the ring-closing olefin metathesis (RCM) to the unsaturated 1,4-dioxamacrolides. Insight into the structure-odor relationship (SOR) is provided by the synthesis of ten related unsubstituted or methyl substituted oxamacrolides. Finally, a four step enantioselective synthesis of both (3R)-(+)- and (3S)-(-)-3-methyl-1,4-dioxacyclopentadecan-2-one as well as (3R)-(+)- and (3S)-(-)-3-methyl-1,4-dioxacyclohexadecan-2-one reveals that mainly the (3R)-(+) enantiomers are responsible for the powerful musky odor characteristic. Their synthesis starts from ethyl (2S)-2-hydroxypropanoate (14) or isobutyl (2R)-2-hydroxypropanoate (15) which were treated under acidic conditions with allyl trichloroacetimidate (16), followed by titanate mediated transesterification, ring-closing olefin metathesis and hydrogenation.
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Marcus Eh (2003) studied this question.