Diazo alkanes synthesis

A simple synthesis of some 1,1-dialkyIcyclopentadienes (234) has used the 1,3-dipolar addition of diazo-alkanes to 3,4-dichlorocyclobutene. The resulting pyrazo-lines were converted quantitatively into the bicyclo[2,l,0]pentanes (235) by photo-chemically induced loss of nitrogen sodium-naphthalene dechlorination gave the cyclopentadienes, by way of the bicyclo[2,l,0]pentenes. Dehalogenation of (235) with Fe2(CO)g gave the diene-iron tricarbonyl complexes (236) directly. 

A cyclic iminocarbene was transferred from 2-diazo-5-isopropyl-3,6-dimethoxy-2,5-dihy-dropyrazine to an alkene under unusually mild conditions. This diazo compound decomposes under the conditions of its synthesis from 2,5-dihydropyrazine 8, and in the presence of cy-cloalkenes, 2,5-dihydrospiro[pyrazine]bicyclo[n.l.O]alkanes 9 (n = 3-5) were obtained (an experimental procedure is given in Houben-Weyl Vol. E19b, pi 194). 

Transition metal catalyzed decomposition of unsaturated a-diazo ketones or a-diazo esters is a powerful method for the synthesis of certain 2-oxobicyclo[n.l.0]alkanes. In contrast to the thermal (see Section 1.2.1.2.4.2.6.1.) and photochemical (see Section I.2.I.2.4.2.6.2.) methods, which have only been applied successfully in a few cases, the carbenoid version has been extensively utilized for the construction of simple or highly substituted bicyclic, tricyclic or higher systems of predictable stereochemistry (for reviews, see refs 2, 82, 320). Several of the cyclopropanes so obtained have been transformed further into natural products with diverse molecular skeletons. As examples and procedures have already been presented in Houben-Weyl, Vol. E19b, ppl088ffand 1271 ff, only some important aspects concerning the scope and limitation of the method as well as recent developments concerning its stereochemistry will be discussed here. 

For the same reason, Chapter 2 includes little information on the synthesis of diazoalkanes containing a heteroatom group at the diazocarbon atom (e.g., l-diazo-l-5-alkanes with S=—S —, — SO —, — SO2 —, 1-diazo-N-alkanes and 1-diazo-l-P-alkanes), because the preparations of these diazoalkanes would have to be treated in several sections of this chapter besides some specific syntheses. Bdhshar et al. (1990) have already discussed them comprehensively (1-S-derivatives p. 1292, 1-A p. 1307, l-P p. 1316). 

---