Transition-metal carbene complexes are promising reagents for electrophilic cyclopr~panations.l-~ Earlier we had shown that (CO)5W=CHC6H5 could be generated at -78 OC from (CO)5-WCH(OCH3)C6H~ and was a reagent for the selective formation of cis cy~lopropanes.~ We were interested in developing a reagent for transfer of the dimethylcarbene group as a route to gem-dimethylcycl~propanes.~ The use of (CO)5W=C(CH3)2 appeared impractical since reaction of (CO)5W=C(OCH3)CH3 with nBuLi gave predominantly deprotonation rather than addition6 and since generation of (CO)5W==c(CH3)C6H5 led to rapid hydrogen migration to give (CO)5W(styrene) and other product^.^ Stable dimethylcarbene complexes ((C5H5)(CO),M=C(CH3), (M = Mn, Re)) have been prepared by Fischers but there has been no report of their reaction with alkenes. On the basis of work by Pettit,9 B r o~k h a r t ,~, '~ Helquist,2J1 and Cutler,12 (C5H5)-(C0)2Fe=C(CH3)2+ (1) appeared to offer greater promise as an electrophilic cyclopropanating agent than organotungsten reagents.
This experiment describes the synthesis of a family of fragrances, including the commercially important Methyl Diantilis, that were covered by a U.S. patent in 1987. The first step in the synthesis is the reduction of 3-ethoxy-4-hydroxybenzaldehyde (ethyl vanillin) to 3-ethoxy-4-hydroxybenzyl alcohol (ethyl vanillyl alcohol). In the second step, etherification of 3-ethoxy-4-hydroxybenzyl alcohol yields 3-ethoxy-4-hydroxybenzyl methyl ether (Methyl Diantilis). Using either ethanol, 1-propanol, or 2-propanol in the etherification step yields the corresponding 3-ethoxy-4-hydroxybenzyl alkyl ethers, which also were described in the patent. All of the 3-ethoxy-4-hydroxybenzyl alkyl ethers have pronounced olfactive notes. This experiment also provided an excellent introduction to intellectual property laws.Procedure updated June 2008. See Letter re: this article.
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