Crotyldiisopinocampheylborane

Z)- and (E)-Crotyldiisopinocampheylboranes, Ipc2BCH2CH=CHCH, (1). Brown and Bhat1 have prepared the two (Z)-crotyldiisopinocampheylboranes [derived from (-)- and (+ )-pinene] by reaction of (Z)-crotylpotassium with the methoxy-diisopinocampheylboranes. The (E)-crotyldiisopinocampheylboranes are prepared in the same way from (E)-crotylpotassium. 

Boron trifluoride etherate, 43 Chlorodimethoxyborane, 73 Crotyldiisopinocampheylborane, 86 Crotyltriisopropoxytitanium, 214 Lithium l-(dimethylamino)naph-thalenide, 165... 

S)-2-Ethoxy-4-isopropyloxazoline, 129 Homoallylic alcohols Crotyldiisopinocampheylborane, 86 Dichlorobis( 1 -phenylethoxy) -titanium(IV), 12 Organotitanium reagents, 213 Tin(II) trifluoromethanesulfonate, 301 Homopropargylic alcohols Bis(2,4-dimethyl-3-pentyl) tartrate, 36... 

Related Reagents. fi-Allyl-9-borabicyclo[3.3.1-nonane B-Allyldiisocaranylborane fi-Allyldiisopinocampheylborane B-Crotyldiisopinocampheylborane (f ,f )-2,5-Dimethylborolane. 

The use of enantiopure allylic boranes in reactions with achiral aldehydes results not only in high diastereoselection, but also in high enantioselectionP Pure (Z)- and )-crotyldiisopinocampheylboranes can be prepared at low temperature from (Z)- or E) crotylpotassium and S-methoxydiisopinocampheylborane, respectively, after treatment of the resultant ate-complexes with BF3 OEt2. The R-methoxydiisopinocampheylboranes are prepared by reacting (-)-diisopinocampheylborane, derived from (+)-a-pinene, or (+)-diisopinocampheylborane, derived from (-)-a-pinene, with methanol. 

The reaction of the (Z)-crotyldiisopinocampheylborane derived from (+-)-a-pinene with aldehydes at -78 °C, followed by oxidative workup, furnishes the corresponding j yn-P-methylhomoallyl alcohols with 99% diastereoselectivity and 95% enantioselectiv-ity. Use of (Z)-crotyldiisopinocampheylborane derived from (-)-a-pinene also produces 5yn-alcohols with 99% diastereoselectivity but with opposite enantioselectivity, an example of reagent control. 

Treatment of ( )-crotyldiisopinocampheylborane, derived from (-r)-a-pinene, with aldehydes furnishes, after oxidation, the ann-alcohols with 95% enantioselectivity. The reaction of ( )-crotyldiisopinocampheylborane, derived from (-)-a-pinene, with aldehydes yields the enantiomeric anr/-alcohols, also with 95% enantioselectivity. By this approach, using cw-and trans-l-hni ne, and (+)-a-pinene and (-)-a-pinene, all four stereoisomeric homoallyl alcohols may be obtained. 

Crotyldiisopinocampheylborane. IpC2BCH2CH=CHCH3 (1). The (Z)-isomer is prepared by reaction of (Z)-crotylpotassium with methoxydiisopinocampheylbo-rane [obtained from (- )-a-pinene] to form an ate complex, which is converted into (Z)-l on reaction with BF3 etherate at -78 . The (E)-isomer is prepared similarly from (E)-crotylpotassium. Reaction of acetaldehyde with (Z)-l at - 78° results in (2S,3S)-3-methyl-4-pentene-2-ol (2) in 99% diastereoselectivity and 95% enantioselectivity (equation I). A similar reaction with (E)-l provides (2S,3R)-2. 

Allylation of aldehydes and ketones and related electrophiles using allyldialkylboranes continues to stimulate interest, especially within the context of asymmetric synthesis. All four possible diastereomeric 3-methylhomoallyl alcohols corresponding to (149) and (150) may be prepared in a highly selective manner using either Z- or E- crotyldiisopinocampheylboranes (147) and (148) and by controlling... 

Related Reagents. Allyl trifluorosilane crotyl trichlorosUane allyl tributylstannane allyl trimethylsilane allylcyclopentadienyl [ 4R,trans)- and (45,rrans)-Q, Q, Q, o -tetraphenyl-l,3-dioxolane -4,5-dimethanolato-0,0 ]titanium fi-allyldiisocaranylborane diisopropyl 2-allyl-l,3,2-dioxaborolane-4,5-dicarboxylate diisopropyl 2-crotyl-l,3,2dioxaborolane-4,5-dicarboxylate fi-allyldi-isopinocampheylborane fi-crotyldiisopinocampheylborane. 

The synthesis of 108 began with homoallylic alcohol 114. Protection of the alcohol was followed by ozonolysis to give aldehyde 115. Reaction of the aldehyde with Z-crotyldiisopinocampheylborane, a chiral crotylborane, gave 116 in high yield with excellent diastereo- and enantioselectivity (see Calcimycin-13... 

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