Aldol reactions 9- -9-borabicyclo nonane

Organoaluminum reagents, 202 1,1,1-Trifluoroacetone, 323 Trityllithium, 338 Zinc chloride, 349 Stereoselective aldol reactions With boron enolates Boron trichloride, 43 Chlorodimethoxyborane, 73 9-(Phenylseleno)-9-borabicyclo-[3.3.1]nonane, 245 With silyl enol ethers... 

Two dialkyl boranes arc in common use. The bicyclic 9-borabicyclo[3.3.1] nonane (9-BBN), introduced in Chapter 34 as a reagent for diastereoselcctive aldol reactions, is a stable crystalline solid. This is very unusual for an alkyl borane and makes it a popular reagent. It is made by hydroboration of cyclo-octa-1,5-diene. The second hydroboration is fast because it is intramolecular but the third would be very slow. The regioselectivity of the second hydroboration is under thermodynamic control. 

Aldol reaction between a silyl enol ether and an aromatic or aliphatic aldehyde can be catalysed by tetrabutylammonium fluoride ketones and epoxides are not attacked by the enolates derived in this manner. Directed cross-aldol reactions have now been carried out by conversion of a methyl ketone into the intermediate (15) using 9-trifluoromethylsulphonyl-9-borabicyclo[3,3,l]nonane and t-amine prior to reaction with the second carbonyl compound. ... 

Lithium tri-sec-butylborohydride, 21 B-3-Pinanyl-9-borabicyclo[3.3.1]-nonane, 249 Sodium borohydride, 21 (3-Hydroxy esters and lactones By aldol-type reactions (R)-( + )-f-Butyl p-tolylsulfinylace-tate, 59 Cadmium, 60... 

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