B-allyldiisopinocampheylborane

Hanessian reported the synthesis of enantiomerically pure or highly enriched allylglycine and its chain-substituted analogs from the reaction of the sultam derivatives of O-benzyl glyoxylic acid oxime with ally he bromides in the presence of zinc powder in aqueous ammonium chloride (Eq. 11.41).72 Brown noticed the critical importance of water in the asymmetric allylboration of /V-trimethylsilyIbcnzaldimines with B-allyldiisopinocampheylborane.73 The reaction required one equivalent of water to proceed (Eq. 11.42). 

Asymmetric hydroboration 2171 of prochiral alkenes with monoisopinocampheyl-borane in the molar ratio of 1 1, followed by a second hydroboration of non-prochiral alkenes with the intermediate dialkylboranes, provides the chiral mixed trialkylbo-ranes. Treatment of these trialkylboranes with acetaldehyde results in the selective, facile elimination of the 3-pinanyl group, providing the corresponding chiral borinic acid esters with high enantiomeric purities. The reaction of these intermediates with base and dichloromethyl methyl ether provides the chiral ketones (Eq. 130)2l8>. A simple synthesis of secondary homoallylic alcohols with excellent enantiomeric purities via B-allyldiisopinocampheylborane has been also reported 219),... 

Related Reagents. B-Allyldiisopinocampheylborane Chlo-ro(T -cyclopentadienyl)[(4/ ,fra 5)-2, 2-dimethyl-a,a,a, a -tetraphenyl-1, 3-dioxolane-4,5-dimethanolato(2—)-0 , 0 ]ti-tanium Chloro(cyclopentadienyl)bis[3-0-(l, 2 5,6-di-0-isopro-pylidene-a- D-glucofuranosyl)]titanium Diisopinocampheyl-boron Trifluoromethanesulfonate Diisopropyl 2-Allyl-l,3,2-di-oxaborolane-4,5-dicarboxylate (4/ ,5/ )-2,2-Dimethyl-4,5-bis-(hydroxydiphenylmethyl)-1,3-dioxolane 2,2-Dimethyl-a,a,a, a - tetraphenyl-l,3-dioxolane-4, 5-dimethanolatotitanium Diiso-propoxide. 

Homoallylic amines. Water is critical in the asymmetric allylboration of N-trimethylsilylbenzaldimines with B-allyldiisopinocampheylborane. 

Asymmetric allylboration of aldehydes containing an adjacent ester group with B-allyldiisopinocampheylborane, followed by hydrolysis and cyclization, provides the corresponding co-allyllactones in high yields and > 92% enantiomeric excess. Hydrogenation of these lactones provides the corresponding w-propyllactones without any loss of optical purity (Scheme 5) (7). 

Our synthesis of ( )-(-)-Argentilactone began with asymmetric allylboration of 2-octynal with (+)-B-allyldiisopinocampheylborane, followed by the stereoselective hydrogenation of the alkynenol in the presence of Lindlar catalyst. This was then converted to the corresponding acrylic ester, and cyclized by refluxing in dichloromethane in the presence of 10 mol% of Grubbs catalyst to provide the natural enantiomer in 44% overall yield (Scheme 8) (9). 

In conclusion, we have reviewed the utility of the products from allylboration of aldehydes with B-allyldiisopinocampheylborane for the synthesis of lactones of varying ring sizes. This is yet another example of the versatility of organoboranes in asymmetric syntheses. 

Typical experimental procedure for the preparation of B-Allyldiisopinocampheylborane 9 and its subsequent allylboration with aldehydes AUyhnagnesium bromide (1.0 mol) is added drop-wise to a stirred solution of B-chlorodiisopinocampheylborane (IPC2BCI, 25) or B-methoxydiisopinocam-pheylborane (IpC2BOMe, 26) (1.05 mol in 1 L ether) at 0 C. After the completion of the reaction as monitored by B NMR (5 79), the reaction mixture is filtered under nitrogen and concentrated under... 

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