Metalloles cycloadditions

Aromatic groups on the ring carbons stabilize strongly the C-phenylated group 14 metalloles, as in the case with phospholes109, but the reactivity of the dienic system (i.e. Diels-Alder cycloadditions, formation of transition metal complexes) decreases3,4. 

The cycloaddition reactions involving group 14 metalloles have been extensively reported in the previous review123. Here we summarize the main points, and give new results. 

MA cycloaddition to metalloles seems to be always stereospecific and, according to Alder s rule, the endo configuration has been attributed to the adduct125. When two different groups R1 and R2 are present (equation 43), the major adduct results from the sterically more suitable transition state, i.e. the more bulky group is preferentially syn with respect to the C=C bond of the norbornene6,67c. 

Metalloles easily react with dienophiles to give [4+2] cycloaddition products. A computational study of the cycloaddition reaction of silole with acetylene was performed <2002JMT(589)291>. It is shown that the silole has the lowest activation energy among five-membered conjugated heterocycles containing C, N, P, O, and S. 

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