Diazoalkanes, cycloaddition with regioselective addition

Whereas the Rh2(OAc)4-catalyzed addition of diazoalkanes to propargyl alcohols readily gives the insertion of the carbene into the 0-H bond, with only a small amoimt of cyclopropenation of the resulting propargylic ether [54] the 2-diazopropane 59 reacts at 0 °C with l,l-diphenyl-2-propyn-l-ol 62a in dichloromethane and exclusively gives, after 10 h of reaction, only the adduct 63a isolated in 75% yield and corresponding to the regioselective 1,3-dipolar cycloaddition of the 2-diazopropane to the alkyne C - C bond (Scheme 15). 

Cycloadditions of i) azides with acetylene equivalents N=N=N + C=C] or ii) diazoalkanes and amide equivalents [C=N=N + C=N] continue to be used for the synthesis of monowclic 1,2,3-triazoles. Notably, diazoalkanes add to 3,5-dichloro-2H-l,4-oxazin-2-ones (/8) and 3-chlorobenzoxazin-2-ones (81) to afford [l,2,3]triazolo[5,l-c]-[l,4]oxazin-4-ones (79) and [l,2,3]triazolo[5,l-c][l,4]benzoxazin-4-ones (82), respectively. These adducts are further modified to the triazoles (80, 82-83). The regioselectivity of this method is opposite to that for the azide addition to nonsymmetric acetylenic acceptors which give predominantly 4-substituted isomers. Addition of azide, in lieu of diazoalkanes, affords the corresponding 1,5-disubstituted tetrazoles [94TL(35)9767]. 

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