Diynes hydroboration

Similarly 9-BBN differentiates between the internal and the terminal triple bonds (Eq. 5.41) of diynes, hydroborating only the terminal carbon-carbon triple bond. 

Condensation of triallylborane with octa-l,7-diyne (130-140 °C, 3 h) followed by treatment with methanol afforded a mixture of stereoisomeric l,4-bis(3-methoxy-3-borabicyclo[3.3.1]non-6-en-7-yl)butanes 66a and 66b (Scheme 26). Hydroboration of the latter with H3B-THF in THF and heating under reflux for 2 h gave rise to a mixture of racemic bis-l-boraadamantanes 67a and meso-ioim 67b in 94% overall yield. Pure racemate 67a was isolated by crystallization from the reaction mixture (THF) and converted to the pyridine complex 64 whose structure was established by X-ray diffraction analysis. 

The THF adduct 70 (mp 147 °C) and pyridine adduct 71 (mp 178°C) of bis-l-boraadamantane with one CH2 bridge were synthesized by hydroboration-cyclization of the bis-bicycle 72, available from hepta-l,6-diyne (Scheme 28) . 

N. Matsumi, M. Miyata, and Y. Chujo, Synthesis of organoboron Tr-conjugated polymers by hydroboration polymerization between heteroaromatic diynes and mesitylborane and their light emitting properties, Macromolecules, 32 4467-4469, 1999. 

The a,p-acetylenic ketones can be synthesized in good yields by the selective mono-hydroboration-oxidation process of conjugated diynes. The monohydroboration of conjugated diynes with disiamylborane places boron preferentially at the internal triple position of the diyne system. The resultant organoboranes on treatment with sodium hydroxide and 30% H202 afforded the a,P-acetylenic ketones (Eq. 33) 79). 

Table 1. Hydroboration Polymerization of Aromatic Diynes Using Mesilylborane. ...

Hydroboration followed by oxidation provides an indirect route for hydration of diynes and constitutes an efficient route to acetylenic ketones as demonstrated by the synthesis of 206 in 75% yield from diyne 205... 

Conjugated diynes can be reduced to cis enynes by the well-known hydroboration-protonolysis sequence . cw-5-Dodecen-7-yne (215) is obtained from the diyne 213 in 76% yield as shown in equation (23). The orientation of addition of the disiamyl-borane was established by using CH3CO2D in the second step. Addition of a second mole of disiamylborane to 214 is very slow, but reduction to the cis,cis diene can be accomplished by using dicyclohexylborane instead . 

Diynes can lead to enynes or to dienes depending on the dialkylborane chosen as the hydroborating agent, the stoichiometry and the substitution pattern of the diyne e.g. equations 64 and 65). ... 

Hydroboration of a,co -diynes with boron tribromide yielded (equation 43) a novel type of organoborane polymer (45) with reactive B—Br groups, which is a poly-Lewis acid. ... 

A wide range of novel polymers with boron in the backbone have been prepared by means of boration polymerizations (65,70-82). Diynes can be polymerized by hydroboration (70,71), phenylboration (65), and haloboration (72) to yield polymers (14),(15), and (16) (eq. 17). When an appropriate aromatic or heteroaromatic diyne is used, the resulting polymers have been shown to have extended 7T-conjugation through the vacant p-orbital of the boron atom (73,74). In fact, several have been shown to exhibit blue fluorescence emission. 

Selective hydroboration of symmetrical conjugated diynes with dialkyl-boranes provides a route to acetylenic ketones in yields >70%. Protonolysis of the intermediate boranes also gives the corresponding c/5-ene-ynes in high yield (Scheme 2). ... 

The enantioselective synthesis of axially chiral P—N ligands was also accomplished by rhodium-catalyzed [2 + 2+-2] cycloaddition. The reactions of 1,6-diynes 75 with diphenylphosphinoyl-substituted isoquinolinyl acetylenes 76 furnished diphenylphosphinoyl-substituted axially chiral 1-arylisoquinolines 77 with high yields and ee values (Scheme 9.28) [23], The new diphenylphosphinoyl-substituted axially chiral 1-arylisoquinoline 77 (Z = NTs, R = Me) was derivatized to the corresponding axially chiral P—N ligand 78 and isoquinoline A-oxide 79 without racemization, which could be used in the rhodium-catalyzed hydroboration and Lewis base-catalyzed allylation, respectively [23],... 

Acetylenes are known to be reactive toward hydroboration reaction as well as dienes. Accordingly, hydroboration polymerization with monoalkylborane can also be applied to diynes. Generally, the reactivity of a terminal acetylene group toward hydroboration is quite different from that of an internal acetylene group. That is, the terminal... 

---