Propenyl allyl derivatives

Recently, an additional version of intramolecular aglycone delivery starting from 2-O-allyl derivatives and using iodonium ion-promoted tethering was described [83]. As illustrated in Scheme 5.28, the 2-(9-allyl ether (154) was first isomerized to the propenyl ether (155). NIS-promoted coupling with the acceptor (146) then afforded the mixed acetal (156), which was transformed into the (3-mannoside (148) by using NIS and AgOTf for activation. 

Eykman (Ber. 1889, 22, 3172) concluded from an optical examination of a mixture of asarone and safrole that the former is a propenyl and not an allyl derivative, and the constitution of asarone was finally determined by Gattermann and Eggers (Ber. 1899, 32, 289) by synthesizing asarylic aldehyde (ii) from 1 2 4-trimethoxybenzene and then heating this aldehyde with propionic anhydride and sodium propionate, when asarone (iii) was obtained in a yield of 60 per cent. Asarone melts at 62-63° and boils at 296°, specific gravity at 18°, 1.165. 

The 8-allyl derivative of 56 can be rearranged to the respective propenyl derivative of 57 by the action of sodium ethoxide (93KGS1545) (Scheme 17). 

Propenyl from O-allyl derivatives OCHgCH CHg OCH CHCHg... 

Potassium tert-butoxide/dimethyl sulfoxide 0-Propenyl from 0-allyl derivatives Allyl as protective group... 

Table 2 summarizes the results obtained with l,3-dialkyl-2-propenyl acetates - a class of substrates for which enantioselective allylic alkylations have not been reported yet [53]. Here, the ligand with a tert-h xiy group at the stereogenic center gave the best enantioselectivities. The 1,3-dimethyl and 1,3-di-n-propyl-allyl derivatives react with dimethyl malonate under mild conditions to afford the expected products in high yields with -70% ee. The 1,3-diisopropyl derivative was... 

O-Propenyl from O-allyl derivs. OCH2CH CH, OCH CHCH ... 

The first evidence for the existence of a discrete 2-propenyl cation in the gas phase was from the results of thermochemical measurements of the heat of formation of this ion by equilibrium proton transfer to propyne. The heat of formation for the 2-propenyl cation derived from these measurements is sufficiently different from that for the allyl cation to suggest that this vinyl cation is stable to rearrangement to its more stable allylic isomer. This rearrangement barrier is calculated to be 74.9 kJ mol , consistent with the high barrier implied by these experiments. This structural conclusion has been confirmed by a number of more direct experimental methods in the gas phase. ... 

A recent reporP on the photochemistry of the 3-(l-naphthyl)propenyl acetate derivatives 12 (Scheme 3 yields normalized to 100%) is clearly related to the arylmethyl ester reactivity. Along with rearranged acetate and to 2 isomerization, photosolvolysis in methanol results in the ethers 13. Two observations are surprising First, no ethers resulting from trapping of the aUylic cation at the terminal end were reported, and, second, no products derived from allylic radical intermediates were observed. 

Freparatively useful induced diastereoselectivities have been reported mainly for 1,1-di-substituted allyllithium derivatives which bear carbanion-stabilizing substituents. l-[Methyl-thio-l-(trimethylsilyl)-2-propenyl]lithium106 and the appropriate 1-phenylthio107 derivative, generated from the allylic sulfide with sec-butyllithium, in the reaction with tetrahydropyranyl-protected pregnolone, furnish a single diastereomer. 

Finally, 2-allyl-4,5-tra ,s-diphenyl-l,3-bis(4-methylphenylsulfonyl)-l,3,2-diazaborolidincs have been used74. The 2-propenyl derivative undergoes highly stereoselective reactions with achiral aldehydes (95 - 97% ee) the ( )-2-butenyl derivatives (91-95% ee) and the analogous 2-chloro- and 2-bromo-2-propenyl derivatives (84-99% ee) also give excellent results in reactions with achiral aldehydes. 

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. 

Nucleophilic addition to a, -unsaturated sulfones has long been known. For example, treatment of divinyl sulfone with sodium hydroxide has been known to afford bis( -hydroxyethyl) sulfone "", while the reaction of a- and -naphthyl allyl sulfones and allyl benzyl sulfone " with alkali hydroxide or alkoxide gave -hydroxy or alkoxy derivatives. In the latter reaction, the allyl group underwent prototropy to the 1-propenyl group, which in a subsequent step underwent nucleophilic attack . Amines, alcohols and sulfides are known to add readily to a, -unsaturated sulfones, and these addition reactions have been studied widely. In this section, the addition of carbon nucleophiles to a, ji-unsaturated sulfones and the reactions of the resulting a-sulfonyl carbanions will be examined. 

The following table lists common names, position of ring substitution, and approximate activity of the amphetamine derivatives for some readily available allyl and propenyl benzenes (see J. Chromatography 30,54(1967) for further information on these compounds). Activity is relative to mescaline which equals 1 (an activity of 12 means a dose of about 25 mg). Parentheses indicate a methylenedioxy bridge other substituents are methoxy groups. 

From equation 10 with phenyl lithium as the benchmark species, RLi, and the hydrocarbon compounds, R H, in their reference gaseous states, the derived enthalpies of formation of allyl, ii-l-propenyl, 2-propenyl and ethyl lithium, are —12.8, —7.3, 54.3 and —58.3 kJmoP, respectively. The first and last of these are remarkably consistent with the values in Table 1. 

The synthesis of (S)-ibuprofen (S)-34 utilizing allylic alkylation was undertaken to determine the stereochemical course of this process. The reaction of the enantiomeri-cally enriched allylic carbonate (S)-32 (95% ee) with the requisite aryl zinc bromide (Scheme 10.7) [32], under optimized reaction conditions, furnished the 3-aryl propenyl derivative (R)-33 in 90% yield (2° 1°=10 1) with inversion of configuration (100% cee). The synthesis of (S)-ibuprofen (S)-34 was then completed through the oxidative cleavage of the aUcene (R)-33 in 74% yield [33]. 

The present method offers a more efficient and convenient two-step route to the parent a,B-unsaturated acylsilane derivative. The first step in the procedure involves the conversion of allyl alcohol to allyl trimethylsilyl ether, followed by metalation (in the same flask) with tert-butyllithiura at -75°C. Protonation of the resulting mixture of interconverting lithium derivatives (2 and 3) with aqueous ammonium chloride solution furnishes (1-hydroxy-2-propenyl)trimethylsilane (4), which is smoothly transformed to (1-oxo-2-propenyl)trimethylsilane by Swern oxidation. The acylsilane is obtained in 53-68% overall yield from allyl alcohol in this fashion. 

Treatment of the (—)-menthone-derived 2/7-1,3-benzoxazin-4(3//)-one 202 with triflic anhydride gave the triflate 203 in quantitative yield. Palladium-catalyzed cross-coupling of 203 with 2-pyridylzinc halide resulted in formation of an approximately 3 1 mixture of the 4-(2-pyridyl)-2//-l,3-benzoxazine 204 and a 4-imino-l,3-benzodioxane derivative 205 (Scheme 36). Compound 205 was formed by the isomerization of 203, which occurred with complete retention of stereochemistry. The 4-(2-pyridyl)-l,3-benzoxazine derivative 204 was applied in enantioselective allylic alkylations of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate as a chiral ligand inducing a 62% ee in the product <2005JOM(690)2027>. 

Allylic a-bromo boronic l,l,2,2-tctramethyl-l,2-ethanediyl esters are too labile to permit preparation in high stereochemical purity. Finacol l-bromo-2-propenylboronate with sodium methoxideyields 1-methoxy-2-propenyl boronic l,l,2,2-tetramethyl-l,2-ethanediyl ester54. Attempted conversion of the corresponding chloro boronic ester to alkoxy derivatives failed54. 

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