Organoborierung von Alkinylstannanen, XVIII. Neue kondensierte heterocyclische Systeme aus N- und C-lithiierten Azolen und cis- 1,2-organometallisch substituierten Alkenen/ Organoboration of Alkynylstannanes, XVIII. Novel Fused Heterocyclic Systems from N- and C-Lithiated Azoles and cis-1,2-Organometallic Substituted Alkenes

Abstract

Abstract Organoboration of dimethyl(chloro)-1-propynylstannane with triethylborane gives (E̲)-2-dimethyl(chloro)stannyl-3-diethylboryl-pent-2-ene (2a) in high yield. Reactions of 2a with N- and C-lithiated azoles (pyrazole, 1-m ethylimidazole, 1-methyl-1,2,4-triazole) lead to the new fused heterocyclic systems 8, 10, 12. In the case of 10 and 12 it was possible to detect (by 11B, 119Sn NM R ) the isomers 9 and 11 which have a zwitterionic structure with an Sn-N linkage. After heating, the compounds 9 and 11 rearrange quantitatively into 10 and 12, respectively. These results show the com petition between boron and tin in 2a as electrophilic centres.