Alcohols synthesis using organoboranes

Some one-carbon donors in alcohol and ketone synthesis using organoboranes... 

One case study within the framework of this project is thus to test the concept of a micro structured reactor plant by applying the fast reaction of the enantioselective synthesis via organoboranes yielding chiral-substituted alcohols. This is typically a batch process carried out in the laboratory using conventional glassware and in the present case has been converted into a continuous process carried out by micro structured devices. This set-up has been used to characterize the physical properties of the backbone system. 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

B-l-Alkenyl-9-borabicyclo[3.3.1]nonanes (1). These substances are prepared by hydroboration of alkynes with 9-BBN (2, 31 3, 24-29 4, 41 5, 46-47 6, 62-64). -Allylic alcohols. Usually reaction of organoboranes with carbonyl groups results in reduction. However, B-l-alkenyl-9-borabicyclo[3.3.1.]nonanes (1) add to simple aldehydes to give, after oxidation, allylic alcohols, with retention of configuration (equation I). The reaction is a Grignard-like synthesis and should be a useful route to allylic alcohols, even to those containing functional groups. 

A useful transformation in synthesis is the reaction of an organoborane to form a carbon-carbon bond. One method to achieve this is by addition of carbon monoxide, followed by oxidation, which can be directed to give primary, secondary or tertiary alcohols, aldehydes or ketones under appropriate conditions. On heating, many... 

A general synthesis of cyclopropylboranes has been developed and its use as a stereocontrolled route to substituted cyclopropanol derivatives demonstrated.The reaction of lithium dichloro-methane with organoboranes has been studied systematically with a view to preparing homologated primary and secondary alcohols. ... 

Two migrations from boron to carbon occur when the products of reactions of organoboranes with acyl carbanion equivalents are treated with electrophiles. A useful synthesis of secondary alcohols is shown in reaction (8), whilst in a similar way (82) provides a route to 1,1-dialkylethanols (HCl as electrophile). ... 

It should be noted that in the synthesis of primary alcohols only one of the three alkyl groups in the organoborane is converted to product. This disadvantage can be overcome by using a dialkylborane, particularly 9-BBN, in the initial hydroboration. The monomigration product can also be worked up under mildly oxidative conditions to give aldehydes.The carbonylated intermediate can... 

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