Allyl type organometallic intermediates allow the prepn. of the 4'-oxa analogs I (R = H, OH, X = O) of a-santalene (I; R = H, X = CH2) and a-santalol (I; R = OH, X = CH2) in a very convenient, regio- and stereocontrolled manner from bromotricyclene (II). The introduction of the heteroatom into the side chain of the natural fragrances changes the smelling properties profoundly. [on SciFinder (R)]