Cyclic propargylic alcohol

Protons on the 8 carbon of a ruthenium allenylidene complex are acidic, and deprotonation at this position often occurs to give ene-yne derivatives. Reaction of I with cyclic propargyl alcohols of type 110, for example, did not yield the allenylidene complexes, but rather the ruthenium ene-yne products (111) were isolated [Eq. (97)] (78). Reaction of the cor-... 

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... 

These reactions are thought to proceed by initial formation of the lithio propargylic alcohol adduct, which undergoes a reversible Brook rearrangement (Eq. 9.14). The resulting propargyllithium species can equilibrate with the allenyl isomer and subsequent reaction with the alkyl iodide electrophile takes place at the allenic site. An intramolecular version of this alkylation reaction leads to cyclic allenylidene products (Eq. 9.15). 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

Cycloaddition between Propargylic Alcohols and Cyclic 1,3-Dicarbonyl Compounds... 

Recently, the electrochemical behavior saturated alcohols, that is, propargyl alcohol (HCSCCH2OH, PA) [145], benzyl alcohol (C6H5CH2OH, BA) [146] andallylalcohol [147], has been studied at Pd electrodes in an acid medium by cyclic voltammetry, chronoamperometry, and on-line mass spectrometry. For BA, it was observed that the fragmentation of the molecules occurs at potentials in the hydrogen ad-sorption/absorption region of palladium, whereas for PA the adsorbates maintain the C3-chain. On the other hand, the yields of the electroreduction and electrooxidation products for both PA and BA differ from those obtained at Pt [146,148,149]. 

The procedure described in this experiment exemplifies a general method [225] for the reduction of propargylic alcohols to -allylic alcohols. The first step in the reaction is the formation of the aluminium alkoxide -C=C-C-OAlH3. Subsequently one of the three hydrogen atoms attached to aluminum is transferred to the triple bond with formation of a 5-membered cyclic aluminum compound. Hydrolysis affords the -allylic alcohol. In the present case an -enyne alcohol is formed. 

Primary amines react with propargylic alcohols and C02 in a different way, such that the reaction may afford cyclic carbamates. The reaction of u-propylamine with C02 and HC=CCH(R)OH (R = H, Me) in the presence of Ru3(CO)i2 gave... 

Synthesis of Cyclic Carbonates from Propargylic Alcohols... 

Cyclic carbonates have also been synthesized from propargylic alcohol derivatives and C02 as the starting materials. This synthetic approach (Equation 7.22) is based on cyclization of the propargylic carbonate moiety (HC=CCH20C02-) into the corresponding a-alkylidene CC, in the presence of a suitable catalyst such as ruthenium [202], cobalt [203], palladium [204, 205], copper [206-211], or phosphine [212-214],... 

Recently, Ikarya has reported the use of imidazolin-2-ylidenes with N-alkyl and N-aryl substituents and their C02 adducts as catalyst of the carboxylative cydiza-tion of internal and terminal propargylic alcohols [215], The reaction of internal propargyl alcohols with C02 has been carried out also under supercritical conditions. Ikariya et al. have developed a synthetic process to afford Z-alkylidene cyclic carbonates promoted by P( -C4H9)3 with high efficiency [216],... 

The reaction of propargylic alcohols and sc C02 in the presence of a trialkylphosphine as a catalyst gave cyclic carbonates in an excellent yield (Ikariya and Noyori, 1999). Dixneuf reported that the reaction proceeded without solvent, but not in nonpolar solvents such as toluene. The reaction efficiency in sc C02 was superior to that in solution phase (Fournier et al., 1989 Journier et al., 1991). The TON reached 1200 and the TOF exceeded 400. The sufficient concentration of C02, as well as the high reactivity of the ion-pair intermediate in sc C02, is responsible for such high efficiency. 

Intramolecular hydrosilylation. The hydrodimethylsilyl ether (2) of a homo-propargyl alcohol (1) undergoes intramolecular hydrosilylation catalyzed by H2PtCl6 to give a cyclic (E)-vinylsilane (3). This can be converted to a 0-hydroxy ketone (4) by hydrogen peroxide oxidation or into (Z)-3-bromo-3-decene-l-ol (5) by brom-ination/bromodesilylation with inversion of geometry. 

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