Regioselectivity of 1,1-dimethylallene allylboration: synthesis of isomeric 6- and 7-methylene-3-borabicyclo[3.3.1]nonanes

Selective Metal‐free HB(C6F5)2 Catalyzed Allene Cyclotrimerization: Formation of 1,3,5‐Trimethylenecyclohexane and Its Tris‐hydroboration Product

“…We assume that areaction pathway similar as depicted in Scheme 3i sf ollowed here,o nly that the hydroboration and carboboration reactions all preferentially take place at the unsubstituted allene = CH 2 terminals (for ar espective reaction Scheme see the Supporting Information). Consequently, ap air of 1 HNMR resonances were observed for the =CH 2 hydrogen atoms of C 3,5 We have started to look for new applications of the now easily available allene cyclotrimerization product 1,3,5-trimethylenecyclohexane (3a)and found aremarkable outcome of its reaction with the hydroboration reagent HB(C 6 F 5 ) 2 .F or this purpose we generated compound 3a by our catalytic process in CD 2 Cl 2 in situ (24 h, 60 8 8C) and then determined the amount of formed product 3a by NMR spectroscopy with an internal standard. Careful addition of three molar equivalents of HB(C 6 F 5 ) 2 (in CD 2 Cl 2 solution) at room temperature gave the tris-hydroboration product 14,w hich we isolated as aw hite solid in 59 %yield.…”

“…Thermolysis of allene (1a)w as reported to give complicated mixtures of oligomers, [2,3] among them some 1,2,4-cyclotrimer 2 but not the 1,3,5-isomer 3a.1 ,3,5-Trimethylenecyclohexane (3a)h ad been prepared stoichiometrically starting from alkyl boraadamantanes. [4][5][6] Them etalcatalyzed oligomerization of av ariety of substituted allenes gave complicated mixtures.A ne xception is the bulky tertbutyl allene that gave a13% yield of the 1,3,5-trimer 4a plus higher oligomers or polymers in a( Ph 3 P) 4 Ni 0 catalyzed process. [7] Recently,agold-catalyzed cyclotrimerization of aminosubstituted allenes giving 4b (as am ixture of stereoisomers) was reported.…”

Design of Bicyclic and Cage Boron Compounds Based on Allylboration of Acetylenes with Allyldichloroboranes

“…Obviously, allylic borane used at the first stage must be able to allylborate C−C triple bond and bear two functional groups at the boron atom. The reagents of choice for this purpose seemed to be highly electrophilic allyldihaloboranes, capable for allylboration of not only activated multiple bonds but also allenes, acetylenes, , and even simple alkenes , as well.…”

“…The starting allyldichloro- and methallyldichloroboranes were generated in situ by the redistribution reaction of triallyl- or trimethallylborane with BCl 3 . , Allylboration of propyne with AllBCl 2 readily proceeds under mild conditions (−78 °C). The penta-1,4-dienyldichloroborane formed initially was detected and characterized by 1 H, 13 C, and 11 B NMR and IR spectroscopy of the reaction mixture.…”