Hydroboration defined

The properties of these new materials are being studied. Hydroboration is also appHed for the conversion of double bonds in polymers into hydroxyl groups (450—454). Well-defined copolymers of ethylene—vinyl alcohol can be prepared (455). 

A variety of organoboron polymer electrolytes were successfully prepared by hydroboration polymerization or dehydrocoupling polymerization. Investigations of the ion conductive properties of these polymers are summarized in Table 7. From this systematic study using defined organoboron polymers, it was clearly demonstrated that incorporation of organoboron anion receptors or lithium borate structures are fruitful approaches to improve the lithium transference number of an ion conductive matrix. 

The hydrides 44b have been found to polymerize ethylene and react with a variety of protic reagents such as terminal alkynes and nitriles. Catalytic effects in the hydroboration of olefins have also been observed [27]. A well-defined /i-ethynyl complex of yttrium is formed by protolysis of the alkyl derivative 38b with acetylene (Eq. 18). Figure 14 shows the dimeric structure of 45b with bridging ethynyl ligands [27, 65]. 

The currently available methods for the synthesis of the title compounds are confined to the preparation of homo-1,1-dihalo-1-alkenes 180 while only a few reports are available for mixed 1,1-dihalo-1-alkenes of defined stereochemistry 18u. As the hy-droboration reaction proceeds in a stereospecific manner, the hydroboration-oxi-dation-bromination-debromoboration sequence of 1-chloro-l-alkynes produces selectively (Z)-l-bromo-l -chloro-l-alkenes (Eq. 116),82>. The oxidation with anhydrous trimethylamine oxide of the alkenylborane prior to the addition of bromine is necessary to avoid the competing transfer of one of 1,2-dimethylpropyl group from boron to the adjacent carbon atom. Similar reaction sequence provides 1,1-dibromo-l-alkenes (Eq. 117)182). 

Finally, well-defined boron-containing polymers by dehydrocoupling reactions have been prepared for a hydroboration reaction (Figure 22.7d) [28, 29]. These polymers can be readily obtained in mild conditions without generating water or other by-products. This synthetic route is preferred because it avoids the hydrolysis and disproportionation of boron-containing polymers. Recently we examined a... 

AUylboranes, which are available from organometallics or by hydroboration, undergo oxidation without aUylic transposition and with retention of stereochemistry. This applies Irath to regio- and stereo-chemically defined allylic dialkyIboryP and allylic dialkoxyb P compounds (equations 14 and 15). 

A number of atypical reactions of enamines have been developed. For example, hydroboration-oxida-tion affords stereochemically defined, vicinal amino alcohols (equation 26). Similarly, enamines have been shown to undergo reaction with diazomethane to form substituted cyclopropanes. These materials can be further transformed to a alkylated ketones by thermolysis followed by hydrolysis (equation 27). ... 

Masamune and cowoikers designed a set of chiral rra/iy-2,5-dimediylborolane-based reagents diat show remarkable enantioselectivities in hydroboration, ketone reduction and crotyl addition to aldehydes. The chirality transfer also turns out to be highly efficient in the aldol reaction. Initial experiments were aimed at defining the structural parameters which affect the E(0) Z(0) ratios of the enolates prepared from various alkanethioates with 2,5-dimethylborolanyl triflate (90) under standard conditions... 

Hydrotitanation of 1-silyl- and I-stannyl-1-alkynes leads to P-silyl (or p-stannyOalkenyltitanates, thus showing opposite regioselectivity to other related processes (hydroboration, hydroalumination, hydromagnesiation, hydrotitanation, hydrozincation, hydrozirconation).Well-defined alkenes are obtained on further reaction of the alkenylti-tanates, for example, with allylic carbonates an 8 2 displacement occurs to afford 1,4-di-... 

Alkenylboron derivatives are readily available by stereo-defined hydroboration of alkynes and used for the preparation of styrene derivatives by alkenyl-aryl coupling. Vinylboronic acid (81), the most simple alkenylboronic acid, is difficult to handle, because it undergoes uncontrollable polymerization. Its anhydride, 2,4,6-trivinylcyclotriboroxane (82)-pyridine complex, is stable, and can be used conveniently for the coupling. Vinylation of 2-bromoanisole with 82 proceeds in refluxing DME using K2CO3 as a base fo provide 2-vinylanisole (83) [80]. 

Define each term, and give an example, (a) dimerization (d) stereospecific addition (g) Markovnikov addition (j) hydrogenation (m) heterogeneous catalysis (p) hydroxylation (s) hydroboration (v) oxymercuration-demercuration (y) alkoxymercuration-demercuration... 

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