Prenyl ether

Useful selectivity between allyl and 3-methylbut-2-enyl (prenyl) ethers has been achieved. ... 

Rearrangement of allyl ethers. Treatment of isopentenyl prenyl ether 2 with 1 results in formation of the two C n)-alcohols 3 and 4 in a 1 3 ratio. Use of other Lewis... 

The palladium-catalyzed hydroboration of allyl phenyl ether 456 is followed by cyclization of the corresponding triflate to afford the chroman core of the tocopheryls 457 (Equation 186) <1998JA9074>. The intramolecular hydroarylation of l-(but-3-enyloxy)-3,5-dimethylbenzene to afford 4,5,7-trimethylchroman can be accomplished using a RuCh/AgOTf catalytic system (Equation 187) <20040L581>. 2,2-Dimethylchromans 458 are formed by a Mo(CO)6 catalyzed intramolecular cyclization of aryl prenyl ethers 459 (Equation 188) <1998S256>. 

In the laboratory, however, the route from prenyl ethers or thioethers to artemisia compounds and thence to the santolina skeleton is possible, and an interesting conversion to the lavandulyl skeleton of prenyl compounds has been described. A mixture of 3-methylbut-2-enyl acetate (44) (or chloride) and 3-methylbut-2-enylthiol acetate (45) is treated with aluminium chloride or zinc chloride, when, in addition to the thioether (46), 19% of the lavandulylthiol acetate (47) and 6% of the corresponding isolavandulyl compound (48) are formed. An ingenious two-step synthesis of trans-chrysanthemyl alcohol (49) has also been achieved from prenyl alcohol (50) and 3-methylbut-l-yn-3-yl... 

Dihydrobenzofurans and 2,2-dimethylchromans. Cyclization with skeletal rearrangement is observed when aryl allyl ethers are heated with Mo(CO)j in toluene, for example, aryl prenyl ethers give 2,2-dimethylchromans. ... 

Functional group cleavage. Prenyl ethers and A-Boc amides are cleaved with Yb(OTf)3 as catalyst. 

Prenyl ethers can be formed using the typical Williamson ether synthesis—that is, by reacting the alcohol with a suitable base and a prenyl halide. Many of the methods used for the formation of allyl and benzyl ethers should be applicable. ... 

DDQ, CH2CI2, H2O, rt, 0.75 min to 9h, 36-89% yield. The reaction can be run using catalytic DDQ with Mn(OAc)3 as the reoxidant. AUyl, TBS, TBDPS, and a phenolic prenyl ether were stable to these conditions. ... 

I2, CH2CI2, 3A ms, 1-8 h, rt, 22-94% yield. The Bn, allyl, and TBDMS ethers are stable to these conditions, but TBS ether is partially cleaved. Phenolic prenyl ethers react to give chromanes. 

The ester is prepared using DCC/DMAP (90-97% yield). It is cleaved in a two-step process wherein the prenyl ether is removed with DDQ in CH2CI2/H2O to reveal an alcohol that is induced to lactonize with Yb(0Tf)3-H20 releasing the protected alcohol 90-92% yield). ... 

The section on the formation of allyl ethers should be consulted, since many of those methods are applicable to the prenyl ether. One difference is that the phenolic OH is more acidic, thus weaker bases may be used in methods that rely on an 8 2 process. 

Pd(Ph3P)4, PMHS, ZnCl2, THF, rt, 89-92% yield. Allyl ethers and esters are cleaved similarly, but a prenyl ether is stable. 

Fluorine substituents on the C—C double bond greatly accelerate Claisen rearrangement. For instance, difluorovinyl prenyl ether 83 rearranges at 100°C, while nonfluorinated vinyl prenyl ether rearranges at 200°C [ 1 ]. The chemoselective transformation of 76 to 75 reveals also a favorable fluorine-directed rearrangement [2]. 

Photolysis of coumarin-3-carbonylazides gives nitrenes in the triplet state, and these have been trapped by hydrocarbons and by aniline. Prenyl ethers of 3-hydroxycoumarins undergo an abnormal Claisen rearrangement and give the 4-allyUc compound (193), but, in the presence of an 8-methoxy-group, the side-chain is further rearranged as in (192). ... 

Prenyl ether cleavage. The cleavage shows preference to ethers possessing a proximal coordinative site to allow chelation control. 

The synthesis starts from the A-Boc-tyrosine methyl ester, which was O-benzylated, since the prenyl ether required in the target compound is not compatible with the conditions required for the preparation of the hydoxylamine or the hydrogenation of the isoxazolidine intermediate (Scheme 40). Following cleavage of the A-Boc, the resulting primary amine was treated with anisaldehyde, and after oxidation with m-CPBA... 

The acetate shown in acetone containing potassium carbonate (with some, 18-crown-6), then after Ih reflux the prenyl chloride added and refluxing ( Ah) continued to give the 5-0-prenyl ether... 

As found (refs. 16,28), bis Cg prenyl derivatives of orcinoi can also give rise to isomeric tricyclic benzodipyrans such as the two compounds depicted. Certain of the remaining components of the reaction mixture could be isomeric mono O-prenyl C-prenyl compounds which in turn would be expected to afford 5- or 7-prenyl ethers of 2,2-dimethylchromans and the presence of C/0 triprenylorcinols and their transformation products might be anticipated. 

Atrovenetin, (Table 12.1), herqueichrysin are related phenalones (ref. 59) and are unusual in that they both contain a trimethylfurano moiety arising from an prenyl ether since there is no 2-hydroxyl group to form a chromene ring from an adjacent C-prenyl group. Synthetic work (ref.59) has led to members of the group by the Claisen rearrangement. Thus the prenyl ether of the phenalone intermediate in DMF at 100°C directly afforded atrovenetin trimethyl ether. 

The occurrence of (1,1-dimethylallyl)- and (l,2-dimethylallyl)quinoline derivatives in Flindersia and Ravenia species and the isolation of the prenyl ether 261 from Ravenia (Section V,B) suggested that the biosynthesis of this group of alkaloids might proceed via Claisen and abnormal Claisen rearrangements as in the synthetic route (Scheme 22, Section V, B). 

Support for this proposition was provided by preliminary 14C-feeding experiments with R. spectabilis whereby it was shown that the prenyl ether 261 (ravenine) is a precursor of ravenoline 265 (0.75% incorporation)... 

Prenyl ethers can be cleaved under mild conditions (1.2 equiv DDQ, 9 1 CH2Cl2 water) without cleaving other alcohol protect-... 

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