Origin of thermodynamic versus kinetic control of allene hydroboration with 9-borabicyclo[3.3.1]nonane and 10(r)-trimethylsilyl-9-borabicyclo[3.3.2]decane

Organic Letters

Volumn 11, Issue 23, 2009, Pages 5538-5541

  Ess, Daniel H ^a   Kister, Jeremy ^a   Chen, Ming ^a   Roush, William R ^a  

^a SCRIPPS RESEARCH INSTITUTE   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKADIENE; ALKANE; ALLENE; BORON DERIVATIVE; DECANE; NONANE;

ARTICLE; CHEMICAL STRUCTURE; CHEMISTRY; KINETICS; THERMODYNAMICS;

ALKADIENES; ALKANES; BORON COMPOUNDS; KINETICS; MOLECULAR STRUCTURE; THERMODYNAMICS;

EID: 72449183590     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol902364d     Document Type: Article

References (17)

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8. (b) The S-configuration of 1a was used in all calculations.
9. Jaguar, version 7.5; Schrodinger, LLC: New York, 2008. All stationary points were verified as minima or first-order saddle points by calculation of the full Hessian. Enthalpy and free energy corrections were applied at 298 K and all energies are reported in kcal/mol.
10. This level of theory gives energetics in agreement with CCSD(T) theory for [1,3]-boratropic shifts. See:Choi, J. Y.; Kim, C. K.; Kim, C. K.; Lee, I. J. Phys. Chem. A 2002, 106, 5709.
11. The other extreme on a closed-shell More O'Ferrall-Jencks diagram would be a charge-separated boracyclobutane. Between the ground state and TS, the NBO charges change most significantly at the boron center, which loses positive charge.
12. In both TS-Z6 and TS-E6, allene 2c approaches the borane face opposite of the 10-TMS group. Hydroboration from the side nearest the 10-TMS group is disfavored by ∼3 kcal/mol. Also see: Ess, D. H.; Kister, J.; Chen, M.; Roush, W. R. J. Org. Chem. 2009; DOI: 10.1021/jo901737d.
13. 2BH hydroboration of 1,1-disubstituted allenes shows high kinetic control. See: Chen, M.; Handa, M.; Roush, W. R. J. Am. Chem. Soc. 2009, 131, 14602.
14. Substituent effects on the barrier for the [1,3]-boratropic shift of dimethyl borane is given in the Supporting Information.
15. NBO 5.0; Glendening, E. D., Badenhoop, J. K., Reed, A. E., Carpenter, J. E., Bohmann, J. A., Morales, C. M., Weinhold, F., Eds.; Theoretical Chemistry Institute, University of Wisconsin: Madison, WI, 2001; http://www.chem.wisc.edu/ ~nbo5.
16. The C-Si bond length decreases by only 0.004 Å between Z-7 (1.930 Å) and TS-Z7 (1.934 Å). The barrier for rearrangement of TS-Z7 decreases by 6.4 kcal/mol when the 10-TMS group is deleted and replaced with hydrogen. When the 10-TMS is is deleted and replaced with SiH3, the barrier is intermediate between TMS and hydrogen because there is both a small hyperconjugative effect and reduced steric interactions.
17. Sarotti, A. M.; Pellegrinet, S. C. J. Org. Chem. 2009, 74, 3562.