2- Pentyne reaction with carbene complexes

The reaction with 4-pentyn-l-ol gave only [Fe t/2-CH2=C(CH2)30) (CO)2(t/-C5H5)]+, and 3-hexyn-l-ol afforded (64, R = Et) (84) no evidence for the participation of the vinylidene tautomers was found. With ruthenium (45) and platinum (47) complexes, on the other hand, rearrangement to the vinylidene is faster than internal attack on the >/2-alkyne, and only the cyclic carbene complex is formed. 

A more general approach concentrates on the chiral modification of the carbene ligand. Some examples based on a chiral carbene carbon side chain are depicted in Figure 4. [68] The reaction of alkoxy- and amino(cyclohexenyl)carbene complexes with 1 -pentyne afforded diastereomeric tetralin complexes in moderate yields. [69] The sense of stereoselection was found to depend on the substitution pattern of the cyclohexenyl substituent. Whereas 5-methyltetralin derivatives were obtained in low preference for the syn complex, a higher preference for the anti diastereomer was observed synthesizing the 8-methyltetralin complexes 50 (Scheme 27). [69]... 

It is noteworthy, in the present case, that, unlike with simple alcohols, there is no reaction between the alcohol function and the triple bond of the carbene metal complex. Similarly, 4-pentyn-l-ol (entry 5) gave 5b from its reaction with lb as the main product and a major organic adduct related to 6 as side product (not yet fully characterized). 

Crucially, it was found22 that upon reaction of the vinylketene complex 42.a with 1-pentyne, the same product distribution was seen as for the direct thermolysis of 1-pentyne with the precursor carbene 43.a. The analysis was simplified by reduction of the crude reaction mixture with McMurry s reagent to produce a mixture of the isomeric indanols 44-46. 

Thus, reaction of chromium carbene 77 with 1-pentyne followed by exposure to air provided biaryl 78 having the (aS,7S) relative configuration in 40% yield and as a single diastereoisomer. Starting from regioisomeric complex 79 resulted in the formation of a mixture of both... 

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