Cyclohexenylboration of Aldehydes and Ketones with the Borabicyclo[3.3.2]decanes (BBDs).
Asymmetric hydroboration of 1,3-cyclohexadiene with 4R produces the allylborane 5RR as essentially a single diastereomer (i.e., no observable 5RS), and its addition to representative aldehydes provides 9RS (52-75%) with excellent selectivity (94-99% ee). By contrast, a similar sequence with the 10-Ph-BBD reagent, 14R, results in a ca. 45:55 mixture of 15RR and 15RS. However, their addition to methyl ketones provides the corresponding 3°-homoallylic alcohols (18RS) with excellent selectivity (80-99% ee) but in low yields (15-52%) because 15RS is unreactive toward either allylboration or isomerization to 15RR. Thus, with 2 equiv of 15, the yield of 18 (R = Ph) is increased from 52% to 85%. Boranes 5SS and 15SS provide enantiomeric alcohols.
Department of Chemistry, University of Puerto Rico , Rio Piedras, PR 00931-3346, United States.
Eduvigis
E
González
Department of Chemistry, University of Puerto Rico , Rio Piedras, PR 00931-3346, United States.
Lorell
L
Muñoz-Hernández
Department of Chemistry, University of Puerto Rico , Rio Piedras, PR 00931-3346, United States.
Eyleen
E
Alicea
Department of Chemistry and Biochemistry, University of California, Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
Bakthan
B
Singaram
Department of Chemistry, University of Tennessee , Knoxville, Tennessee 37996-1600, United States.
George W
GW
Kabalka
Department of Chemistry, University of Puerto Rico , Rio Piedras, PR 00931-3346, United States.
John A
JA
Soderquist