Propyne photoaddition

Bos and coworkers have developed several applications of alkyne-ketone photoadditions to organic synthesis. 2 Irradiation of a solution of acetone and 1-methylthio-l-propyne gives as a major product the cycloadduct (67) this results from selective oxetane formation due to radical stabilization by the methyl-thio group, followed by electrocyclic ring opening. Similarly, photoreaction of benzil and 1-t-butylthio-1-propyne gave the adduct (68) in 45% yield, which was transformed in 90% yield to the furan (69). 

The use of silica gel surfaces to modify photoprocesses continues to be of interest. The present report deals with photoaddition of alkenes to the steroidal enone (44).It is presumed that, in the adsorbed state on silica gel, the steroid will present the normally hindered side, i.e., the g-face is attacked by the alkene and the a-face is adsorbed on to the gel. The photoadditions were compared with those carried out in methanol. Thus with allene the two photoproducts (45) and (46) were obtained in 90 and 10% yields, respectively, at -78 °C in methanol, while on silica gel, both at -78 °C and at ambient temperature, the same two products were obtained in 46 and 53% yield. Similar results were obtained using ethene and cyclopentene. The photocycloaddition of ethyne and propyne to progesterone and testosterone in solution yields the cycloadducts (47) and (48), with a preference for the former mode of addition being observed. These results are in conflict with those of de Mayo and co-workers. ... 

The regiospecific formation of the cyclobutene-type adduct (261) has been reported as a result of the photoaddition of diphenylacetylene to the cyanouracil (262). The cycloaddition of 1-phenylprop-l-yne to the same substrate is reported to yield the cyclobutene (263) as the main product when Pyrex-filtered irradiation is used. The irradiation of the same compounds using 254 nm light afforded the novel adduct (264), presumably formed by the secondary cyclization of the initially produced adduct (265). Indeed the sensitized irradiation of the uracil (262) and the propyne yields this adduct (265) as a Z- -mixture as well as the cyclobutene (263). Direct irradiation of (265) affords the cyclized compound... 

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See also in sourсe #XX -- [ ]

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