3- Aryl-2-alkynols

Aryl-2-alkynols In a process mechanistically analogous to the Meerwein-Ponndorf-Verley reduction, transfer of arylethynyl group to certain aldehydes (such as chloral and pentafluorobenzaldehyde) can be achieved via the trialkoxyaluminum species derived from 4-aryl-2-methyl-3-butyn-2-ols and the aluminum reagent [or 12,2 -bipheny lenedioxy-(/-butoxy)aluminum]. 

Recently, a Pd/Cu-catalyzed three-component coupling reaction of aryl halides, norbomadiene, and alkynols was reported to generate 2,3-disubstituted norbomenes in high yields in the presence of aqueous NaOH and a phase-transfer catalyst in toluene at 100°C (Eq. 3.39).151... 

A novel ring-closure starting from 2-aryl-l-(12/-l,2,4-triazol-l-yl)alk-3-yn-2-ols has been reported <2006T8966>. Treatment of these alkynols with Bt2 at room temperature yielded 5-alkyl-7-aryl-6-bromo-7-hydroxy-7,8-dihydro-[l,2,4]triazolo[l,2- ]pyridazin-4-ium bromides which upon hydrolysis give 3-alkyl-5-arylpyridazines. 

The propargyl alcohols react with trivalent phosphorus halides to give allenic phosphorus esters as described in Scheme 3 and Table VI. In the case of aryl-substituted alkynols or highly hindered t-propargyl alcohols which contain no free acetylenic —H, thionyl halides or phosphorus trihalides yield bromo- or chloroallenes [74d], Thionyl chloride also reacts in a similar fashion with a wide variety of unhindered secondary alcohols (structure XV) to give a mixture of the chloroallene and chloroalkyne [74a-d]. 

The anionic complexes (50) are obtained from the group VI carbonyl and the dilithium derivatives of the hydroxyalkynes HC=CCR2(OH) subsequent protonation or acylation affords propadienylidene (51) or carbene (52) complexes by complex cyclization and addition reactions (Scheme 3) (28). Attempts to obtain the dimethyl complex by reaction of the chromium alkynolate dianion with COCl2 gave only polymeric material. More stable complexes were obtained with R = aryl (73). 

Anti-Markovnikov cyclizations For anti-Markovnrkov cyclizations of 4-alkynols to dihydropyrans such as glycals, the catalysts or reagents introduced by McDonald [150] remain synthetically important [151,152]. Another catalyst based on ruthenium was presented by the Trost group. A rather finely tuned catalyst based on a CpRuCl (PAr3)2 complex (Ar = aryl) achieved similar reactions like the McDonald catalyst (Scheme 25c) [153]. 

The direct Au-catalyzed synthesis of 2-arylindoles from aryl alkynes and o-iodoanilines was reported by Wang (eqnation 3) [17]. The An-catalyzed double hydroamination of o-alkynylanilines and terminal alkynes was fonnd by Li to give A-vinylindoles [18], Patil used a Au-catalyzed one-pot reaction between o-alkynylanilines and alkynols to give various 3-substituted indoles [19]. Zhang fonnd that both A-arylhydroxylamines [20] and... 

The catalytic ability of dimeric palladium hydroxide in carbonylative Sonogashira coupling was demonstrated by Alper and his team in 1994 [29]. In this report, terminal alkynes and alkynols were coupled with aryl iodides in the presence of carbon monoxide in moderate to good yields (Scheme 5.6). In 1995 Cacchi and colleagues presented a general methodology for 5-(2-acylethynyl)-... 

The Diels-Alder reactions of -deficient 2//-pyran-2-ones with vinyl moiety containing dienophiles under microwave and high pressures have been extensively reviewed. The microwave-initiated intramolecular Diels-Alder reaction of an alkynol with a furan (80) formed a cycloadduct (81) that readily converted to 3,4-disubstituted 5-hydroxyindoles (82) in 15-74% yields in a one-pot reaction (Scheme 23). ° The treatment of < rt/io-(trifluoromethanesulfonyloxy)aryl boronic acid pinacol ester (83) with t- or i-butyllithium generates arynes (85) via boronate intermediate (84) at... 

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