Facile O-Deallylation of Allyl Ethers via S_N2‘ Reaction with tert-Butyllithium

Abstract

[reaction: see text] Allylic ethers are converted to the corresponding alcohol or phenol in virtually quantitative yield at temperatures below ambient simply by stirring a hydrocarbon solution of the ether with 1 molar equiv of tert-butyllithium. The reaction, which produces 4,4-dimethyl-1-pentene as a coproduct, most likely involves an S(N)2' attack of the organolithium on the allyl ether.

Highly Efficient Deacetylation by Use of the Neutral Organotin Catalyst [tBu2SnOH(Cl)]2

“…To our surprise, however, these triflates were found to be much less active (entries 12 ± 14), and, moreover, the Sn 12 dication 6 exhibited virtually no activity as well (entry 15); this is indicative of a mechanism for which the Lewis acidity is not necessarily of primary importance. Consistent with these results, even stronger Lewis acids were not as effective; various metal triflates failed to afford quantitative yields after 3.5 h (entries 16,17,19,[21][22][23] and, thus, a prolonged reaction time or higher catalyst loading was required for satisfactory yields (entries 18, 20 and 24). [11] Both BF 3´O Et 2 and TfOH were virtually inactive (entries 25 and 26).…”

“…The starting alcohols to acetyl esters 7 ± 11, 17, 18, 21, 23, and 24 were commercially available. Acetyl esters 12, 13, and 15 were prepared from mono-tertbutyldimethylsilyl-protected butanediol [19] and heptanediol, [20] and acetonide-protected propandiol, [21] respectively. Acetyl ester 14 was accessible by acetylation of THP-protected heptanediol.…”

“…However, this outcome involved transesterification of the original methyl ester with solvent methanol as is evident from Acetyl groups from secondary alcohols were less reactive and higher reaction temperatures were needed for quantitative yields (entries 12 ± 20). When the acetyl ester of 8-pentadecanol (19) was subjected to the reaction, only a 32 % yield of the alcohol was recovered even at 50 8C (entry 16). The refluxing conditions increased the yield to some degree but the concomitant elimination was also accelerated (entry 17).…”

Intramolecular Carbolithiation of Allyl o‐Lithioaryl Ethers: A New Enantioselective Synthesis of Functionalized 2,3‐Dihydrobenzofurans

“…Moreover, in these cases around 40 % of phenol was generated as a result of a competitive S N 2' cleavage of the allyl moiety by the excess tBuLi used in the bromine/lithium exchange reaction. [15] We concluded that the 1,3-elimination process is not slow enough compared with the carbolithiation reaction and therefore it is not possible to obtain selectively the dihydrobenzofuran derivatives 5.…”

Regioselective and stereoselective cleavage of cis‐4‐methyl‐2‐vinyl‐l,3‐dioxane by alkyllithiums

“…3,4 More recently, an apparently similar S N 2¢ cleavage of allylic ethers upon treatment with tert-butyllithum in hydrocarbon solvent has been developed as a general method for the removal of an allyl protecting group. 5 Herein we report the results of a study of the reaction of alkyllithiums with cis-4-methyl-2-vinyl-1,3-dioxane (3). As detailed below, treatment of 3 with either n-butyllithium (n-BuLi) or tert-butyllithium (t-BuLi) in a variety of solvents results in a formal S N 2¢ ring opening that proceeds in a regioselective manner via cleavage of the C(2)·O bond remote from the 4-methyl substituent to give the E-enol ether as the major stereoisomer.…”