Propargylic alcohols allylic alcohols from

In this type of study, the terminally-CF3 propargylic alcohol (S)- derived from the enzymatic resolution is also a useful intermediate. This material is transformed into the corresponding E- and Z-allylic alcohols after successful enzymatic optical resolution. Os04-catalyzed oxidation eventually led to the formation of the desired triols 30 in a diastereoselective manner. 

Synthesis of homologated allylic alcohols from propargylic alcohols is easily performed via hydrozirconated intermediates. Chain elongation or functionalization at either end of the original triple bond is feasible because hydrozirconation of the derived alkoxides becomes group-directed. ... 

Allylic and Propargylic Alcohols. Allyl silanes (22), formed as Diels-Alder adducts from 1-trimethylsilyl butadiene, can be converted regiospecifically into allylic alcohols (Scheme 8), either with allylic rearrangement, using peracids, or without rearrangement. The latter transformation is achieved by first reacting the allyl... 

Chromatographic analysis has shown that this inconsistency arises from the presence of various side reactions. Contact of propargyl and allyl alcohols with the palladium - hydrogen system leads to the formation not only of propanol but also propionaldehyde and gaseous products (propane, propylene, and others), although the absolute percentage of the latter is small. At the end of the reaction the products were foimd to contain 68.8% propanol and 31.7% propionaldehyde, i.e., one third of the allyl alcohol formed isomerizes. 

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]. 

Previous syntheses of terminal alkynes from aldehydes employed Wittig methodology with phosphonium ylides and phosphonates. 6 7 The DuPont procedure circumvents the use of phosphorus compounds by using lithiated dichloromethane as the source of the terminal carbon. The intermediate lithioalkyne 4 can be quenched with water to provide the terminal alkyne or with various electrophiles, as in the present case, to yield propargylic alcohols, alkynylsilanes, or internal alkynes. Enantioenriched terminal alkynylcarbinols can also be prepared from allylic alcohols by Sharpless epoxidation and subsequent basic elimination of the derived chloro- or bromomethyl epoxide (eq 5). A related method entails Sharpless asymmetric dihydroxylation of an allylic chloride and base treatment of the acetonide derivative.8 In these approaches the product and starting material contain the same number of carbons. 

The stereochemistry of the first step was ascertained by an X-ray analysis [8] of an isolated oxazaphospholidine 3 (R = Ph). The overall sequence from oxi-rane to aziridine takes place with an excellent retention of chiral integrity. As the stereochemistry of the oxirane esters is determined by the chiral inductor during the Sharpless epoxidation, both enantiomers of aziridine esters can be readily obtained by choosing the desired antipodal tartrate inductor during the epoxidation reaction. It is relevant to note that the required starting allylic alcohols are conveniently prepared by chain elongation of propargyl alcohol as a C3 synthon followed by an appropriate reduction of the triple bond, e. g., with lithium aluminum hydride [6b]. 

This disadvantage can be ruled out by spacers between the allylic and the acrylic group [15], but the selectivity in favor of the allylic group is not improved. An acetylenic triple bond instead helps to clarify the situation. 2-Propynoxyethyl acrylate, available in 90 % yield from ethoxylated propargylic alcohol by esterification, is hydrosilylated very smoothly only at the triple bond, leaving the acrylic side virtually untouched (Eq. 5). 

Under the catalytic action of Rh2(OAc)4, formation of a propargylic ether from a terminal alkyne (229, R1=H) is preferred as long as no steric hindrance by the adjacent group is felt162,218>. Otherwise, cyclopropenation may become the dominant reaction path [e.g. 229 (R1 = H, R2 = R3 = Me) and methyl diazoacetate 56% of cyclopropene, 36% of propargylic ether162)], in contrast to the situation with allylic alcohols, where O/H insertion is rather insensitive to steric influences. 

An important variant for transition metal-catalyzed carbon-nitrogen bond formation is allylic substitution (for reviews, see1,la lh). Nucleophilic attack by an amine on an 7r-allyl intermediate, generated from either an allylic alcohol derivative,2 16,16a 16f an alkenyloxirane,17-19,19a-19d an alkenylaziridine19,19a 19d, or a propargyl alcohol derivative,21,21a 21d gives an allylic amine derivative. 

Still, occasionally the other fuctional groups react as well, for example in 38 under basic conditions the propargylic alcohol isomerizes to the a,/3-unsaturated ketone [73] (Scheme 1.15), whereas in a closely related substrate from the synthesis of a subunit of compactin an allylic alcohol remains unchanged [74],... 

When optically active allylic alcohol 6a and propargylic alcohol 6p were reacted with amides 2c and 2f, only racemic products 7ac, 7af, and 7pf were obtained (Scheme 2). The results suggested a mechanism through the formation of a carbe-nium intermediate. The observed racemization can also be ascribed to the reversibility of the present reaction. The result shown in Scheme 3 indicated that the reaction is reversible under the reaction conditions. When 7af was treated with 5 mol% of Bi(OTf)3 and KPF6 and 1 equiv of carbamate 2c, a mixture of 7af (28%) and 7ac (68%) was recovered after 1 h. The result suggested that Bi(OTf)3/KPF6 cleaved the C-N bond in 7af derived from sulfonamide 2f, and that 7ac is thermodynamically more stable than 7af. We assume that the desiccant (Drierite) had a beneficial effect on the reactions of substrates shown in Tables 10-12 because of the observed reversibility of the present reaction. In this reaction, the possibility... 

Tandem reaction generally attracts much interest because it allows us to effect multiple transformations, all in one pot. Two types are known at present. The most popular approach is a combination of several reactions with PKR. Properly functionalized 1,6- or 1,7-enynes are readily obtained from the propargyl alcohol-dicobalt hexacarbonyl complexes and a properly nucleophilic allylic moiety in the presence of a Lewis acid. The resultant enynes are subjected to the promoter-assisted PKR without purification to afford the desired PKR products (Scheme 9).82,82a-82e... 

In the synthesis of alkylidenecyclobutenes from propargyl alcohols, stoichiometric experiments show that the first step involves [2+2] oxidative head-to-head coupling of the alkynes, leading to an isolable cyclobutadiene-ruthenium complex. Addition of acid generates a cyclobutenyl metal intermediate which undergoes carboxylate addition on the less substituted allylic carbon atom (Scheme 7). 

An intramolecular version of olefin cross-metathesis has been demonstrated in cyclization of a,u -alkadienes 293462 (Equation (85)), cyclization of enyne to provide 1,3-dienylboronic esters 297406 (Equation (86)), and in cyclization of boron-tethered enynes obtained from 1-alkynylboronates and allylic alcohols (298 463 (Equation (87)) or allyl boronates and propargyl alcohols.464... 

A new preparative method for allylic indium(m) reagents via a reductive transmetallation of 7r-allylpalladium(n) or 7T-allylnickel(n) complexes with indium(i) salts is reported. This method enables the use of a wide variety of allylic compounds, such as allylic chlorides, acetates, and even allylic alcohols, in combination with Pd or Ni catalysts.43-50 7r-Allylpalladium(ii) resulting from the addition of arylpalladium(n) to allene is also transformed by metallic indium to the corresponding allylindium.51-54 Similarly, propargylindium(m) can be prepared from the corresponding propargyl alcohol derivatives.55-58... 

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