Propargyl-allenyl anions

Table 2 illustrates 1,3-dipoles with a double bond and with internal octet stabilization, commonly referred to as the propargyl-allenyl anion type. These are all reactive dipoles and a large number of five-membered heterocycles can be constructed from these readily available dipoles, especially when the dipolarophile is varied to include heterocumulenes, etc. 

Table 2 1,3-Dipoles with a Double Bond and Internal Octet Stabilization Propargyl-allenyl Anion Type...

The 1,3-dipoles consist of elements from main groups IV, V, and VI. The parent 1,3-dipoles consist of elements from the second row and the central atom of the dipole is limited to N or O [10]. Thus, a limited number of structures can be formed by permutations of N, C, and O. If higher row elements are excluded twelve allyl anion type and six propargyl/allenyl anion type 1,3-dipoles can be obtained. However, metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions have only been explored for the five types of dipole shown in Scheme 6.2. 

The structure of the propargyl-allenyl anion is still uncertain but by analogy to the carbonium ion above it may be that shown in Eq. (2). 

Sixteen-Electron. Those for which the dipolar canonical form has a double bond on the sextet atom and the other resonance structure has a triple bond. Examples are azides (R—N3), diazoalkanes (R2C=N=N), and nitriloxides (R—C= N—O). These have also been labeled as propargyl/allenyl anion type [270]. 

Table 3 1,3-Dipoles with a double bond and internal octet stabilization propargyl-allenyl anion type...

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