Organometallic Chemistry - UR

[Pages:35]Organometallic Chemistry

Worawan Bhanthumnavin

Department of Chemistry

Chulalongkorn University

Bangkok 10330, Thailand Given as part of the 6th semester organic chemistry course

at the University of Regensburg (May 2008) Under the ASEM-DUO Thailand 2007 exchange program

organoboron, organosilicon

Organoboron compounds

? Revise: what organoboron have you seen before? boranes

Organoboron compounds

? vast array of C-C-forming reactions involving organoborons

? Here: focus on transfer reactions of C moieties from boron to an adjacent C. Examples: transfer of CO, CN, carbanions derived from dichloromethyl methyl ether and dichloromethane, and allyl groups in reactions of allylic boranes with aldehydes.

Preparations

Reaction of Organoborons

Carbonylation

? reaction of organoboranes with carbon monoxide [(?):CO:(+) ], which is an ylide, gives rise to 3 possible rearrangements.

? Depending on reaction conditions, single, double, and triple migrations of groups may occur leading, after appropriate workup, to a variety of aldehydes and ketones as well as primary, secondary, and tertiary alcohols.

Reaction of Organoborons Carbonylation

Synthesis of Aldehydes and Primary Alcohols

? Addition of CO to trialkylboranes leads to the formation of an ate-complex (structure A). Subsequent migration of an R group to the CO ligand yields intermediate B. In the presence of a mild reducing agent, such as lithium trimethoxyaluminum hydride or potassium triisopropoxyborohydride, B is converted to the mono-migration product C.

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