Yne-vinylcyclopropane

The photocycloadditions of 2,3-dimethyl-l,3-diene with 4-(alk-l-ynyl)-substituted coumarins (5) produced a mixture of 4 + 2- and 4 + 4-cycloadducts (6) and (7), respectively. However, the corresponding thiocoumarins (8) yielded a single 4 + 2-cycloadduct (9) (Scheme 2)." The intramolecular photocycloadditions (>290nm) of 1,3-enynes with 2-pyridone yielded 2 + 2- and 4 + 4-cycloadducts. The Rh(I)-catalysed formal 5+l-/2 + 2 + 2-cycloaddition of 1-yne-vinylcyclopropanes (10) with two carbon monoxide units produced multifunctional angular tricyclic 5/5/6 compounds (11) in a one-step mechanism (Scheme 3). ... 

The cycloaddition proceeds efficiently even with methyl substitution of the double bond of the vinylcyclopropane. Although angular alkyl substituents are commonly encountered in natural products and designed targets However, the introduction of such a group has remained a considerable synthetic challenge. Given this situation, it is noteworthy that these new reactions proceed well even when a quaternary center is developed. Cycloaddition of yne-vinylcyclo-... 

Miscellaneous Cycloadditions A rhodium-catalyzed [3-I-2-I-1] cycloaddition of an yne-ene-vinylcyclopropane motif with CO was used for the synthesis of a-agarofiiran. This reaction can be seen as a homologous Pauson-Khand reaction and was found to be quite general, allowing the synthesis of diversely substituted cyclohexenones (Scheme 7.11) [18]. 

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