Secondary propargylic alcohol

The isomerization of propargylic alcohols to a,/3-enones was also developed by using an iridium catalyst. A variety of secondary propargylic alcohols can be isomerized to the corresponding a,/3-unsaturated ketones in the presence of 1 mol% IrHs(Pr 3P)2 (Scheme 54).93... 

Secondary propargyl alcohols (17 R2 = H) require rather stronger acid and a longer reaction time, and the resulting bromoallenes may contain up to 5 per cent of the 3-bromoacetylenes, which may, however, be removed by fractional distillation. 

In contrast with the catalytic system based on RuCl(rf-C9H7)(PPh3)2 in micellar solutions [32], the reaction of secondary propargylic alcohols in 2-propanol/ H20 at 100 °C in the presence of 5 mol % of RuCl(Cp)(PMe3)2 leads to conjugated enals with E stereoselectivity (Eq. 12) [88]. 

The electrophilic propargylation at the C-2-position of furans with propargylic alcohols can be effected by using 5 mol% of the cationic methanethiolate diruthenium complex 41 as a catalyst (Equation 29). Substrates are limited to 1-phenyl-substituted secondary propargylic alcohols <2003AGE1495>. 

The acetals 2 undergo a similar coupling with l-trimethylsilylalkynes, also with high diastereoselectivity, to furnish secondary propargylic alcohols after elimination of the chiral auxiliary (equation 111). ... 

In the laboratory of D. Tanner, a novel method was developed for the stereoselective synthesis of ( )-tributylstannyl-a,P-unsaturated ketones in two steps from secondary propargylic alcohols. The first step was the highly regio- and stereoselective Pd-catalyzed hydrostannylation of the triple bond followed by a mild Ley oxidation. This method was utilized for the construction of a key intermediate for the total synthesis of zoanthamine. 

H. Stark and co-workers prepared novel histamine Hs-receptor antagonists with carbonyl-substituted 4-[(3-phenoxy)propyl]-1/-/-imidazole structures. The Meyer-Schuster rearrangement was used for the synthesis of one of the compounds. The p-hydroxybenzaldehyde derivative was reacted with ethynylmagnesium bromide to afford a secondary propargylic alcohol. Upon hydrolysis with 2N HCI in a refluxing ethanol/acetone mixture, the corresponding p-hydroxy cinnamaldehyde was obtained. 

Chiral 1,3-dialkylallenes. These aUenes can be obtained by reaction of lithium dialkylcuprates with one of the diastereomeric carbamates obtained from racemic secondary propargylic alcohols and the reagent (1). An example is the synthesis of chiral pheromone of the male bean weevil, (R)-( —)-6, as outlined in scheme (I). ... 

The stereochemical outcome of the reaction can be explained by comparison of the relevant transition states of the rearrangement (Scheme 5.2.47). If secondary propargylic alcohols are used, the rearrangement preferentially proceeds via transition state A, where the substituent is oriented in an equatorial position, in comparison to B with in an axial position (Scheme 5.2.47). As expected, the selectivity increases as the size of R increases, because of stronger sterical interactions of the axial R and the chelated enolate in transition state B. 

More recently, Nebra and Gimeno applied this concept to the synthesis of pentasubstituted 3-acylpyrroles 369 from 1,3-dicarbonyl compounds 368 [318]. The efHdency and the scope of this transformation were significantly improved by the use of the Ru(II) catalyst in the presence of trifluoroacetic acid co-promoter. The reaction tolerates 1,3-diketones, (J-ketoesters, various secondary propargylic alcohols 195... 

Determination of Enantiomeric Excesses of Chiral Alcohols, Amines, and Related Compounds. " 10-Camphor sulfonyl chloride continues to be used extensively as a convenient derivatizing agent for chiral alcohols, amines, and related compounds for determination of their enantiomeric access or verification of their optical purity. For example, the secondary propargyl alcohol 15 was converted to the S) 10-camphorsulfonate ester 16 (eq 10) and the de determined by NMR spectroscopy. ... 

Hydrophosphination of secondary propargylic alcohols generates phosphine-containing 0 allylic alcohols that undergo facile [2,3]-sigmatropic rearrangements with chlorophos-phines to give enantioenriched diphosphine monoxides (Scheme 54). 

For the acid-induced cydization of 96 to the furans 97, an allenic intermediate 98 seems to be reasonable. In a comparable Cu(OTf)2-promoted cyclocondensation, secondary propargyl alcohols and 1,3-dicarbonyl compounds afford tetrasubstituted furans [32]. 

Enantioselective formation of secondary propargyl alcohols by the addition of TMSA to the carbonyl group of aldehydes have been reported employing Zn(OTf)2 and A-methylephedrine (eq31). ... 

The asymmetric reducing agent (78) has been used to prepare naturally occurring y-lactones and enantiomerically pure secondary propargylic alcohols,whereas the chiral alkoxy(acyloxy)borohydride(79) gives 35-50% enantiomeric excess in ketone reductions. 

Scheme 3 Reaction of oxabenzonorbomadienes with secondary propargylic alcohols...

SCHEME 10 Ru/TFA-catalyzed coupling of 6-chloro-4-hydroxycoumarin with secondary propargylic alcohols. TFA, trifluoroacetic acid. 

V. Cadierno, J. Gimeno, N. Nebra, Anovel propargylation/cycloisomerization tandem process catalyzed by a ruthenium(U)/trifluoroacetic acid system one-pot entry to fully substituted furans from readily available secondary propargylic alcohols and 1,3-dicarbonyl compounds,... 

The reaction of the cyclic diyne with a commercially available chiral secondary propargyl alcohol afforded a (Rp,R)- or (5 j,i )-cyclophane as a major diastereomer with excellent ee by using (R,R)- or (5,5)-BDPP, respectively, as a ligand (Scheme 8.21) [14],... 

Two new syntheses of 2-pyridones have appeared. The first, involving condensation of ethyl 2-cyanoacrylates, e.g. ArCH=C(CN)C02Et, with an aryl or alkyl methyl ketone in the presence of ammonium acetate, furnishes 4-aryl-3-cyano-5-substituted and -5,6-disubstituted 2-pyridones in moderate yields (21—53%). The second method, which is particularly useful for 6-alkyl-2-pyridones (17 R = alkyl or aryl, R = alkyl), involves thermal rearrangement of the pseudourea (16), obtained by addition of secondary propargylic alcohols, e.g. R CH2CH(0H)C=CR, to 1-cyanopyrrolidine, in boiling xylene (Scheme 3). 

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