Rearrangement of ethers

Rearrangement of ethers upon treatment with alkyllithiums (Wittig)... 

The first enantioselective version was also accomplished with this class of substrates. For example, the rearrangement of ether rac-103 with f-BuLi/bis(oxazoline) 27 afforded ketones 104a and 104b in 48%-50% ee (equation 58) . 

Cleavage of hydroperoxides 8-23 Rearrangement of ethers upon treatment with alkyllithiums (Wittig) 8-24 From boranes and CO, or CN, or CHCEOMe... 

D. Rearrangements of Ethers Containing Monosubstituted Allyl Groups. 39... 

E. Rearrangements of Ethers Containing Disubstituted Allyl Groups. . 43... 

A general [1,2]-Wittig rearrangement of ether 90 is shown below mechanistic studies65 68 70 of the reaction are consistent with formation of a radical pair 94 which rearranges by lithium migration to oxygen to form a product radical pair 95 which then recombines to yield 92. 

MDI is derived from the breakage reaction of the urethane linkage drawn in Scheme 12.1c, the polyester product are formed by intramolecular rearrangement of ether bonds, eliminating cyclic oligomers, and by radical breakage of the polyester chain to partly unsaturated linear oligoethers. 

The rearrangement of ethers with alkyllithium reagents is called the Wittig rearrangement (not to be confused with the Wittig reaction, 16-44) and is similar... 

Hauser noted that diallyl ether (8) also undergoes Wittig rearrangement upon base treatment and suggested that product formation could involve either a 1,2-shift or a cyclic mechanism (equation 3). Later studies by Schdllkopf and Makisumi with substituted allylic ethers (10,11 and 14-16 equations 4 and 5) pointed to a cyclic (SnO mechanism a process allowed by the Woodward-Hoffmann rules. The diastereoselectivity of the reaction was not determined in these cases, but Schollkopf subsequently found that benzyl rrans-crotyl ether (20 equation 6) affords mainly the anti products upon rearrangement of ether (20) with BuLi in THF. Rautenstrauch observed a 1 1 mixture of syn and anti products upon rearrangement of ether (20) in the presence of TMEDA, whereas the cis isomer (23) gave only the syn product (22 equation 7). ... 

The acyclic ethers (264a-c equation 57) failed to give optically active rearrangement products with the nonracemic amide base (-)-(260). Accordingly, the asymmetric induction observed in the rearrangements of ethers (242), (258) and (262) appears to depend upon the chiral environment provided by the cyclic array. 

Intramolecular a-diazo ketone initiated 1,2- and 2,3-rearrangements of ethers, allylic ethers and propargylic ethers E. J. Roskamp and C. R. Johnson,/. Am. Chem. Soc. 1986,108, 6062. 

Wittig rearrangement. Rearrangement of ethers with alkyl lithiums to yield alcohols via a 1,2 shift. 

A striking preference for formation of Z-olefins is observed for the rearrangement of ethers derived from C-2-substituted allylic ethers (e.g., 8)1318-20, a protocol which provides a reliable, stercocontrolled entry to Z-trisubstituled olefins. Olefin selectivity for C-2-substituted systems has been attributed to preferential rearrangement through an RA e d conformation which relieves an eclipsing interaction between RA (the allylic substituent) and the C-2 substituent (vide supra). 

In contrast, metalation and rearrangement of ethers 7 affords a surprisingly high ratio (2 1) of [1,2]/[1,4] products accompanied by significant asymmetric induction at the newly formed stereogenic center50. Despite the modest yields of [1,2] rearrangement products obtained, this protocol provides a useful synthetic entry to stereochemically defined 1,3 diols. 

Other interesting rearrangements of ether derivatives of hydroxy phosphonates have been reported, for example the spontaneous formation of 210 from 209, and the slow... 

A patent has been published that covers the rearrangement of ethers of morphine and N-alkyl-normorphines to the corresponding derivatives of apomorphine and N-alkyl-norapomorphines by phosphoric acid at 125— 140 lO-Oxomorphine has been isolated as an oxidation production from solutions of morphine hydrochloride/ and morphine has been shown to be converted into morphine N-oxide and normorphine by guinea-pig liver microsomal preparations, which convert codeine, under similar conditions, into codeine AT-oxide, norcodeine, morphine, and normorphine/ ... 

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