Alkynes naturally occurring

Organosilicon compounds are widely used in our daily life as oil, grease, rubbers, cosmetics, medicinal chemicals, etc. However, these compounds are not naturally occurring substances but artificially produced ones (for reviews of organosilicon chemistry, see [59-64]). Hydrosilylation reactions catalyzed by a transition-metal catalyst are one of the most powerful tools for the synthesis of organosilicon compounds. Reaction of an unsaturated C-C bond such as alkynes or alkenes with hydrosilane affords a vinyl- or alkylsilane, respectively (Scheme 16). 

Rh-mediated dipolar cycloadditions of diazoquinolinediones 31 with alkenes and alkynes have been investigated. Because of the unsymmetrical nature of the diazo compounds, both linear and angular furoquinoxaline products are possible. In most cases a mixture of tegioisomers was obtained. This methodology has been used for the synthesis of naturally occurring alkaloids, e.g., isodictamnine 32 (R = H) <99JOC3642>. 

The amide [Sm(45a) N(SiMe3)2 ] was a catalyst for an aUene-based hydroamination/ cyclisation. As an illustration, one such product upon hydrogenation yielded a naturally occurring alkaloid. Scheme 4.8. " " The same samarium(lll) amide was also active for the intramolecular hydrophosphination/cyclisation of phosphino-alkenes or -alkynes e.g., H2P(CH2)3C=CPh was transformed into 76. " ... 

In other cases cyclopropenes have been obtained by direct reaction of an alkyne with a diazo-compound in. the presence of a suitable catalyst. Typical of these is the reaction of ethyl diazoacetate with alkynes in the presence of copper, which is reported to lead to about 40-50 % conversion to cyclopropene per equivalent of diazo-compound. This has been applied to the synthesis of the important naturally occurring cyclopropene, sterculic acid, (66) 56) ... 

Ethynylestradiol is a synthetic compound whose structure closely resembles the carbon skeleton of female estrogen hormones. Because it is more potent than its naturally occurring anaiogues, it is a component of several widely used oral contraceptives. Ethynylestradiol and related compounds with similar biological activity contain a carbon-carbon triple bond. In Chapter 11 we learn about alkynes, hydrocarbons that contain triple bonds. 

The Pd-catalyzed coupling reactions of alkenyl bromides with heterocyclic alkynes (40) under the above phase-transfer conditions have been employed to prepare a large number of heterocyclic alkyne derivatives, including some naturally occurring compounds (Scheme 28). The experiment conditions... 

Kobayashi et al. initially proposed a structure shown in the lower part of Figure 6.18 for penaresidin B. Our synthesis of 156 made it possible to critically analyse the 13C-NMR spectrum of the tetraacetyl derivatives of the naturally occurring mixture of penaresidin A and B. Consequently, we proposed 157 as the structure of penaresidin B. Our proposal was confirmed by its synthesis. L-Leucine was converted to alkyne M via epoxide L. The alkyne M yielded 157, whose spectral properties were in accord with those of penaresidin B.21... 

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