Enynes deprotonation

Fluonnated ylides have also been prepared in such a way that fluonne is incorporated at the carhon P to the carbamonic carbon Vanous fluoroalkyl iodides were heated with tnphenylphosphine in the absence of solvent to form the necessary phosphonium salts Direct deprotonation with butyUithium or hthium dusopropy-lamide did not lead to yhde formation, rather, deprotonation was accomparued by loss of fluonde ion Flowever deprotonation with hydrated potassium carbonate in thoxane was successful and resulted in fluoroolefin yields of45-S0% [59] (equation 54) P-Fluorinated ylides may also be prepared by the reaction of an isopropyli-denetnphenylphosphine yhde with a perfluoroalkanoyl anhydnde The intermediate acyl phosphonium salt can undergo further reaction with methylene tnphenylphosphorane and phenyUithium to form a new yhde, which can then be used in a Wittig olefination procedure [60] (equation 55) or can react with a nucleophile [6/j such as an acetyhde to form a fluonnated enyne [62] (equation 56)... 

A more recent application of this chemistry was reported by Oestreich and Hoppe [74] and involved the enantioselective deprotonation of the enyne carbamate ester 125 with sec-butyllithium in the presence of (-)-sparteine (Scheme 2.41). Removal of the pro-S hydrogen atom led to the corresponding organolithium intermediate, which then underwent a highly enantioselective intramolecular 1,4-addition to the enyne. Protonation of the resulting allenyllithium species 126 provided a 70 30 mixture of the two diastereomeric allenes 127. 

Hoppe and Gonschorrek also reported the interesting formation of an enyne structure [137]. Deprotonation of allenyl carbamates 242 bearing a benzoyloxy group caused a 1,4-elimination of lithium benzoate, furnishing 1-alkynyl carbamates 243 in moderate to good yield (Scheme 8.63). 

Use of alkenyl halides in this reaction has proven to be an effective method for the synthesis of enynes.116 117 The reaction can be carried out directly with the alkyne, using amines for deprotonation. 

Thienyllithium derivatives with an alkyl group or H atom at C-5 deprotonate at C-3 with further BunLi in HMPT this leads to ring fission, yielding ene-yne thiolates which can be methylated to form the enyne sulfides. If the mole ratio BuLi/thiophene exceeds... 

Enynals 104 can undergo a palladium-catalyzed cyclization to form the pyrylium intermediate 105, which upon deprotonation affords the triene 106. In the presence of DM AD, a [2+2]-cycloaddition then occurs to form the tricyclic 4//-pyran intermediate 107, which undergoes expansion of the cyclobutene ring to afford the bicyclic 4//-pyrans 108 (Scheme 34) <2004S1409>. 

First the enyne alcohol is converted into the TBS ether via step 1. For introduction of the stannane moiety the alkync is deprotonated by a base, in this case by KHMDS, followed by addition of Bu SnCI. Cis selective reduction of the resulting stannylalkyne is achieved via hydrozireonation using equimolar amounts of CpoZrHCl. This method is not very common and only applied to stannyl alkynes with ether functionalities. Limitation of this method is related to the... 

Phenyl propargyl sulfide " and selenide are rapidly deprotonated by 2 equiv. of base. The resulting dilithio derivatives react at their allylic rather than at their alkynic carbon centers (Scheme 34, entries c and d). Reduction of the sulfides allows the synthesis of 1,5-enynes (Scheme 34, entry b), whereas oxidation of the selenides leads to a-phenylseleno-a,P-unsaturated carbonyl compounds (Scheme 34, entry... 

Treatment of the enyne amine H2C=CH—C=CNMe2 with a catalytic amount of r-BuOK in DMSO or HMPT results in the formation of HC=C—CH=CHNMe2 [116]. The first steps in this isomerization are the vinylic deprotonation at C-3 and subsequent protonation of the trancient anion to give the cumulenic amine H2C—C=C=CHNMe2. It is, however, impossible to achieve any accumulation of this amine, since it is thermodynamically less stable than the ynene amine HC CCH=CHNMe2, and the rate of its conversion into the ynene amine is higher than the rate of its formation from the starting compound. If this is treated... 

In addition to these results, this methodology was successfully applied to the preparation of 3-deshydroxysecu amamine A (222), an unnatural analog of secu amamine (37). The synthesis started from protected piperidone 217 (Scheme 36). Two successive deprotonation/alkylation reactions produced the 2,6-trans product 218 in a good stereoselectivity (>8 1) and modest yield. Then, the ris-enyne side chain was installed in an efficient way by a... 

The isomerization of a deuterated trisubstituted enyne ester formed in the S 2 reaction between an arylalkynylaluminum and trisubstituted allylic phosphates containing an ester group on C(2) in the presence of a Al-heterocyclic carbene-Cu-Brpnsted base catalyst with a >98% retention of the deuterium and a primary hydrogen-deuterium KIE = 3.1, indicating the slow step of the isomerization was deprotonation of the substrate followed by reprotonation on the same face as propargyl hydrogen in the enyne, has been discussed earlier. 

Deprotonation of l,3-bis(trimethylsilyl)propyne with Bu Li and subsequent addition of carbonyl compounds in the presence or absence of an additive such as MgBr2 has been reported to furnish the enyne products with moderate to good Z-selectivity (Scheme 2.84) [235, 236]. It has been reasonably postulated that the reaction proceeds via a kinetically controlled pericyclic process as illustrated by intermediate 134, where steric factors and the interaction between the counter ion and the oxygen atom play major roles. Other additives are also employed in Z-selective enyne formation reactions, such as Ti(OPr )4, B(OMe)3, and B-methoxy-9-borabicydo[3.3.1]nonane (B-MeO-9-BBN) [225, 226, 237-240]. 

Therefore, alternative pathways involving a formal 1,3-hydrogen shift were considered an electrophilic pathway (path II) and a deprotonation/protonation sequence (path III) (Scheme 14.21) [17]. Prototropic rearrangement (path II) is consistent with the effect of Lewis acidic additives. Moreover, substitution at the 2- and 4-positions of enyne (R H) would provide necessary cation stabilization, which is in... 

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