Regioselective Lewis Acid-Mediated [1,3] Rearrangement of Allylvinyl Ethers

Abstract

[reaction: see text]. Aluminum and copper Lewis acids were implemented to effect a regioselective [1,3] rearrangement of allylvinyl ethers in moderate to good yields. The use of trisubstituted alkenes leads to depressed levels of Claisen products.

Palladium-Catalyzed [1,3]-O-to-C Rearrangement of Pyrans toward Functionalized Cyclohexanones

“…A preliminary screening study highlighted Zn(OTf) 2 and Et 2 AlCl as potentially useful promoters, providing 18 in 27% and 40% yields, respectively (entries 2 and 3). At this stage, we decided to confirm that the Lewis acid did not itself mediate the O-to-C rearrangement in a similar manner to that reported by Rovis; only Claisen product 19 was isolated in this case in 47% yield (entry 4). We envisaged that the ionization step could be further facilitated by the use of a polar solvent.…”

A Diastereoselective Ring Contraction of 1,3-Dioxepins to 2,3,4-Trisubstituted and Tetrasubstituted Tetrahydrofurans

“…The use of substituted enol ethers leads to the introduction of a second stereocenter in the process and we showed that in certain cases, useful levels of diastereoselectivity could be achieved (eq 2) . We later showed that allyl cations may be used as electrophile partners in this chemistry in spite of the competing [3,3] using a steric impediment to disfavor the Claisen (eq 3) .…”

“…3 We later showed that allyl cations may be used as electrophile partners in this chemistry in spite of the competing [3,3] using a steric impediment to disfavor the Claisen (eq 3). 4 Alternately, the use of dihydrooxepins as substrates in this reaction also leads to exclusive [1,3] rearrangement with good levels of diastereocontrol (eq 4). 5 Here, the [3,3] process generates a vinyl cyclopropane carboxaldehyde and thus is thermodynamically disfavored relative to the cyclopentene carboxaldehyde product.…”

Enantioselective [1,3] O-to-C rearrangement: dearomatization of alkyl 2-allyloxy/benzyloxy-1/3-naphthoates catalyzed by a chiral π–Cu(ii) complex

“…In 2002 and 2003, Gansäuer demonstrated that, in the presence of catalytic amount of Cu(OTf) 2 , the vinyl ether could lead to [1,3] and [3,3] products in 1 : 1 ratio (Scheme 1a). 7 In the year 2005, Rovis reported the regioselective [1,3] rearrangement of allyl vinyl ether catalyzed by aluminum and copper Lewis acids 8. They mentioned that the rearrangement of trisubstituted alkenes would preferentially produce the [1,3] adduct due to steric congestion for normal [3,3] rearrangement.…”