3-Propynyl compounds

There are two different hydrogens in propyne, and therefore two different ways to produce a substituted compound (Fig. 3.57). When the acetylenic hydrogen is replaced, the compounds can be named either as acetylenes or as 1-propynyl compounds. 3-Propynyl compounds result from replacement of a methyl hydrogen with X. 

Many syntheses of chiral allenes of high enantiomeric purity start from chiral precursors, notably propynyl compounds, with the central chirality being converted into allene axial chirality by a mechanism-controlled reaction. 

Organocopper(I)-mediated syntheses providing allenes from propynyl compounds with high optical yield have been collected in Table 1. 

Table 1. Allenes from Propynyl Compounds by Organocopper(i)-Mediated 1,3-Substitution with Chirality Transfer...

Table 3. Chiral Allenes from Propynyl Compounds by Hydride Transfer from Aluminum Hydride Reagents in THF...

Alkaloids were used as chiral catalysts for the enantioselective prototropic rearrangement of achiral propynyl compounds to chiral allenes with optical purities lower than 1%127. In addition, prototropic rearrangement induced by sodium (-)-mentholate to give the divinylal-lene (M)-l,3,4,6-heptatetraene with op < 1 % is known128. 

Alkenyl(phenyl)iodine(III) compounds can also serve as starting materials in rearrangements. Allenyl(aryl)iodine(III) compounds of type 86 can be synthesized from (diacetoxyiodo) derivatives 85 and propargylsilanes [145]. It depends on the leaving group ability of the aromatic substituent on iodine in 86 as to whether the reaction proceeds via nucleophilic substitution to compounds of type 87 or by an iodonio-Claisen rearrangement to compounds 88, Scheme 37 [146,147]. The easy access to propynyl compounds 87 has been shown [148] and solvent effects in these reactions have been investigated as well [149,150]. 

A number of ethynyl steroids have been synthesized as potential suicide substrates in sterol biosynthesis or as potential antifertility compounds. In the former class were the 19-ethynyl-19-hydroxy-compounds (294) and (295) and the 17-(l-hydroxy-2-propynyl)-compounds (296) and (297). ° Among those in the latter class were the diethynyl-A-nor-compound (298), its 19-nor-ana-logue, and the 18-homo-analogue (299). A number of allenyl compounds... 

Dihydrofurans can be piepaied in good yields (>80%) by the reaction of tungsten i -propynyl compounds with aldehydes in the presence of BF3 etherate in cold toluene (—40°C) (Equation (104)) <92CC934>. 

The molecular structure of di(/M-l-propynyl)bis(dimethylaluminium) has been determined by gas phase electron diffraction. This structure is of interest because of the previously determined structure of diO-phenylethynyl)bis-(diphenylaluminium). In the latter compound the two monomer units (PhaAlC-=CPh) appear to be linked by the donation of two jr-electrons of the C C bond of one unit into an empty atomic orbital on the aluminium of the other unit. The same structure type appears to be adopted by the propynyl compound shown in Figure 1. Thus the Al—A1 bond distance is rather lon than in other... 

The discovery of junipal focused the attention of Sorensen, who had been investigating the occurrence of polyacetylenes in Com-positae, on the possibility that these acetylenes were accompanied by thiophenes. From Coreopsis grandiflora Hogg ex sweet, 2-phenyl 5-(1-propynyl) thiophene (240) was isolated and its structure confirmed by synthesis of the tetrahydro compound, 2-phenyl-5-n-propyl-thiophene. From the root of tansy, the cis and trans isomers of methyl 5-(l-propynyl)-2-thienylacrylate (241) have been isolated. The total synthesis of trans (241) was achieved by reacting junipal with methylcarbethoxy triphenylphosphonium bromide (Wittig reaction) Several monosubstituted thiophenes, (242), (243), and... 

Boiled in a water-dioxane solution in the presence of acids, these compounds turn into l-alkyl-3-propynyl-5-methylpyrazoles (Scheme 25). 

Acetylene Compounds. Part XXV. The Occurrence of Methyl-cis-/5-(5-Propynyl-2-thienyl)-acrylate. Acta Chem. Scand. 13, 1185 (1959). 

The application of this methodology to suitably functionalized alkynes has allowed a direct and easy synthesis of important heterocyclic compounds starting from readily available substrates. New /1-lactone [100,101] and /3-lactam [102] derivatives were synthesized in good yields from a,a-disubstituted propynyl alcohols and amines, respectively (Eq. 38), through the mechanistic route shown in Scheme 18, path a. The substitution a to the triple bond was a necessary requisite for cychzation to occur, owing to the reactive rotamer effect [301]. 

Intramolecular concerted reactions of compounds derived from readily available enantiomeri-cally pure propynyl alcohols12-14 constitute a reliable preparative entry to EPC syntheses of chiral allenes. 

The [2,3] sigmatropic rearrangement of propynyl sulfenates, sulfinates, phosphites and of alkoxypropynyl compounds also constitutes an efficient and stereoselective route to allenes of high enantiomeric purity. 

CM of propynyl benzoate and 1,5-hexadiene is carried out to produce a cyclopentadiene derivative and a triene in 99% yield in a ratio of 1 to 1.2. The former compound is apparently derived from a (Z)-isomer of the triene by further metathesis (Equation (14)). ... 

In many compounds R3 and R4 have been the same, the commonest substituent being methyl,53"10,13,15 17 although examples having ethyl,6,15 2-cyanoethyl,7 2-propenyI,7,11,13 2-propynyI,13 benzyl,7,13 and phenyl15 are also known. Where R3 and R4 are different, R3 has generally been methyl, and exceptionally trideuteriomethyl,18 or ethyl,12,13 whereas R4 has been ethyl,18 2-propenyl,7,13,18 3-methyl-2-butenyl,12,13 2-propynyl,13,18 or benzyl.7,10,13,18... 

This base, MAL, lies as a hybrid of two other compounds, AL and CPM. It is an olefin (as is AL) which means that it has a place of unsaturation in its structure. And it is an isostere of CPM which means that the carbon atoms are all in the same location, but just the connecting electrons (called the chemical bonds) are in different places. Actually there is yet a third compound in this same picture, called PROPYNYL. And yet, although all of them have extremely close structural similarities, there are such great differences in action that one does not dare to generalize. CPM leads largely to fantasy, MAL largely to visual imagery, AL is twice as potent as either of these but it doesn t show either effect, and PROPYNYL is almost without any action at all. 

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