Acetylenic epoxides

Acetylenic epoxides are reduced readily to the olehnic epoxide, provided the resulting epoxide is not allylic (27). In the latter case, one might surmise that hydrogenolysis could best be avoided by use of rhodium in a neutral nonpolar solvent (81) or a Lindlar catalyst (13). Reduction of l,2-epoxydec-4-yne over Lindlar catalyst gave (Z)-l,2-epoxydec-4-ene in 95% yield (69). Hydrogenation ceased spontaneously. 

Another example of this preference is found in the enantiospecific syntheses of tritium-labeled leukotrienes(/i). Commercially available 3-nonyn-l-ol was converted to its phosphorane (16) and Wittig-coupled with the unsaturated aldehyde (17) to afford 18, which was reduced over Lindlar catalyst to give 19. 

The unlabeled esler is made conveniently by reducing ihe Cg acetylene lo ihe olefin before coupling. 

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Some allenic alcohols can be prepared in analogous waysfrom acetylenic epoxides or tetrahydropyrans ... 

The ease with which thiophenes are formed in the reaction of acetylenic epoxides " and of polyacetylenes with hydrogen sulfide is of great interest in connection with the biosynthesis of the naturally occurring thiophenes (cf. Section VIH,A) and also of preparative importance. 2-Methyl-l,2-oxido-5-hexene-3-yne (56) in water containing barium hydroxide reacts with HzS at 50°C to give 4-... 

Formation of Acetylenic Epoxides from the Corresponding Chlorohydrines and KOH... 

Several acetylenic epoxides have been observed to condense with methanol and other alcohols. Addition of methanol to 1,2-epoxy-S-pontyne in the presence of boron trifluoride (Eq, 567), for example, gives... 

Ring cleavage of acetylenic epoxides may be illustrated by the reactions of the substituted 1,2-epoxy-3-butyne derivatives represented in Eq. (023) with ammonia, ethylamine, diethylamjne, and others.1845 1316, isao... 

Addition of a carboxylic acid to an acetylenic epoxide presumably constitutes an intermediate stage in the conversion of 3-methyl-1-phenyl-3-hexen-l-yne into the corresponding 1,2-diol (Eq. 762) by pemoetic acid oxidation.1487... 

Addition of Grignard reagents to acetylenic epoxides is exemplified by the reported condensations of ethylmagnesium bromide and of 1 -bromomagnesyl-5-methoxy-3 -methyl-3-pentea- L-yne with the epoxide depicted in Eqa. (839) and (840). In each case, products isolated... 

Cleavage of epoxides with hydrogen sulfide has been exploited advantageously by Perveev and co-workers < - in the eyn-thesis of certain substituted thiophenes from acetylenic epoxides. Addition of hydrogen sulfide occurs, as anticipated, by attack on the epoxide carbon atom furthest from the triple bond. The resulting... 

Vinylic epoxides such as 2.28 can be reduced by attack on the epoxide carbon atoms according to the usual rules, or they can undergo conjugate reduction, as shown in Figure 2.16 [LKl]. LAH attacks the epoxide at the least substituted carbon, and DIBAH in THF mainly attacks the epoxide at the most substituted one, whereas DIBAH in hexane gives only the conjugate reduction. Acetylenic epoxides are reduced by LAH into homopropargylic alcohols [HDl]. 

Interesting variations of potential synthetic utility include the use of a-acetylenic epoxides and a-allenic alcohol derivatives. " The latter, which can be obtained from the former, have been converted to conjugated dienes for use in the Diels-Alder and other reactions (Scheme 33). 

Grubbs and others " have reported the use of metallocenes attached to crosslinked styrene-divinylben2ene (20%) copolymers. These systems catalyze a wide variety of reactions, including reduction of dinitrogen, isomerization of olefins, hydrogenation of olefins and acetylenes, epoxidation of olefins, and isomerization of cyclodienes. 

Regioselectivity is of particular importance with fundamental starting materials carrying functional groups that offer two reactive positions, such as olefins, acetylenes, epoxides, anhydrides, and imides. There are additionally the two enolate... 

Sutherland and his co-workers have established that tetrasubstituted cyclohexane epoxides can fulfil a useful role as cationic cyclization initiators." Several alk-3-enyl-2,3-epoxy-3-methylcyclohex-2-enones, e.g. (177), have been successfully cyclized to decalone derivatives, e.g. (178), in good yield on treatment with Lewis acids, and the acetylenic epoxides (179) and (181) have been cyclized in excellent yields to the expected decalin (180) and hydrindane (182) derivatives respectively." ... 

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