Theoretical studies of stereoselective hydroborations

Flexible Routes to the 5‐Hydroxy Acid Fragment of the Cryptophycins

“…effected clean elimination to provide the disubstituted allyl ether 22. The stereocenter destroyed in this process was reintroduced by diastereoselective hydroboration, [34,35] which gave the anti product 23 with high diastereoselectivity (9:1). In this case, the introduction of the styrene component was performed by means of a Julia olefination.…”

Assignment of relative configurations and conformational study of acyclic diastereomeric ketones

“…( 5 )-2,2,7,7-Tetramethyl-5,6-diphenyloctan-3-one (1) and (2 )-5,5-dimethyl-l,3,4-triphenylhexan-1-one (2) were obtained by 1,Caddition of 2,2-dimethyl-l-phenylpropylmagnesium chloride to (E)-4,4-dimethyl-lphenylpent-1-en-3-one and (E)-1,3-diphenylprop-2-en-1-one, respectively, in dry tetrahydrofuran.' Pure samples of the respective diastereomeric racemates, (RR, SS) and (RS, SR), conventionally called l a and l b for 1 and 2a and 2b for 2, were separated and purified by fractional recrystallization from methanol for 1 and by silica gel chromatography [30 : 1 (w/w) adsorbent to product ratio] using light petroleum-diethyl ether (97 : 3) as eluent and subsequent recrystallization from methanol for 2.…”

“…'-^ In this context, the conformational analysis and assignment of the relative configurations of chiral acyclic aldehydes and ketones provide very useful structural information. 6 In this paper we report a conformational study and the assignment of the relative configurations [(RR, SS) and (RS, SR)] to the diastereomeric racemates of two acyclic ketones with two asymmetric carbons, ( +)-2,2,7,7-tetramethyl-5,6-diphenyloctan-3-one (1) and ( k )-5,5-dimethyl-1,3,4-triphenylhexan-l -one (2) (Scheme 1). These compounds have previously been employed in the synthesis of /?,/?-disubstituted acyclic u-enones with an asymmetric carbon at the y-position.'…”

Hydroalumination of Cyclopropane: A Transition State Study

“…Houk et al 23,24 and others 25 have examined the reaction path for the analogous hydroboration reaction with a variety of substrates. The intermediates and transition structures found in these studies are consistent with those for the hydroalumination pathway described earlier.…”