Hydrob oration

The conversion of alkenes to amines has a considerable synthetic value and hydrob-oration-amination methodology has been applied using different protocols. However, only two of the three organyl groups can be aminated because of the low reactivity of RB(NHR)2 towards electrophilic nitrogen (equation 2). 

One of the first synthetic applications of organoboranes in radical chemistry is the conjugate addition to enones (Scheme 23, Eq. 23a) and enals reported by Brown [58-61]. Addition to -substituted enones and enals are not spontaneous and initiation with the oxygen [62], diacetyl peroxide [63], or under irradiation [63] is necessary (Eq. 23b). A serious drawback of this strategy is that only one of the three alkyl groups is efficiently transferred, so the method is restricted to trialkylboranes derived from the hydrob oration of easily available and cheap alkenes. To overcome this limitation B-alkylboracyclanes have been used but this approach was not successful for the generation of tertiary alkyl radicals [64,65]. 

The disadvantage of this approach is that since the conversion of the hydrob-oration reaction is not quantitative it is very difficult to have precise control over the number of the PEO arms. Special care should be taken during the hydrobo-ration to avoid side reactions and specifically the crosslinking of the hydroxy-lated polymer. 

MM has been used to study the transition states involved in Sa/2 reactions, hydrob-orations, cycloadditions (mainly the Diels-Alder reaction), the Cope and Claisen rearrangements, hydrogen transfer, esterification, nucleophilic addition to carbonyl groups and electrophilic C/C bonds, radical addition to alkenes, aldol condensations, and various intramolecular reactions [24],... 

Bp3-OEt2 followed hy DiisobutyUduminum Hydride is used for the 1,2-reduction of y-aimno-Q, -unsaturated esters to give unsaturated amino alcohols, which are chiral building blocks for a -amino acids. Q , -Unsaturated nitroalkenes can be reduced to hydroxylamines by Sodium Borohydride and BF3-OEt2 in THF extended reaction times result in the reduction of the hydroxylamines to alkylamines. Diphenylamine-borane is prepared from sodium borohydride, BF3-OEt2, and diphenylamine in THF at 0 °C. This solid is more stable in air than BF3-THF and is almost as reactive in the reduction of aldehydes, ketones, carboxyhc acids, esters, and anhydrides, as well as in the hydrob-oration of alkenes. 

Draw structural formulas for the alcohol formed by hydrob-oration-oxidation of each alkene. 

Hydroboration of Fluoroalkenes. Dibromoborane-dimethyl sulfide (DBBS) has demonstrated to be an excellent hydrob-orating agent. Based upon kinetic and mechanistic studies, it is clear that the hydroboration reaction exhibits a second-order kinetics (detaching of Me2S from the boron center follows a dissociative pathway, while the hydroboration process follows an associative mechanism).DBBS hydroborates a wide variety of alkenes and alkynes. Perfluoroalkylethylenes and 2, 3, 4, 5, 6 -pentafluorostyrene undergo Markovnikov hydroboration (>92% regioselectivity) (eq 12). ... 

This system, thus, provides a method to store the otherwise unstable hydrob-orating agents. 

We can hydrate a double bond in an anti-Markovnikov orientation by hydrob-oration-oxidation (Section 8.7). With hydroboration-oxidation we can also... 

An environmentally benign and simple versatile method for hydroboration-oxidation of alkenes, dienes and alkynes imder microwave irradiation has been explored by Jayakumar et al. (2008). They carried out a simple and facile hydrob-oration-oxidation of alkenes by N,N-dimethylaniline-borane using microwave irradiation. Hydroboration of various alkenes with N,N-dimethylaniline-borane was carried out in dry THF under specially designed microwave apparatus. It was designed to accommodate magnetic stirrer and refluxing condenser with mercury bubbler. Hydroboration was followed by oxidation with HjO /NaOH, which resulted in the formation of corresponding alcohols in 90-95% yield. 

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