Reactions of organoboranes with carbanions bearing three potential leaving groups: unusual processes, products and mechanisms

Abstract

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Reactions between lithiated 1,3-dithiane oxides and trialkylboranes

“…The failure to give more than one boron to carbon migration could suggest that the sulfoxide group might not act as a good leaving group so that the reaction stops after the first migration. However, it could also be that the intermediate 8 formed after the first migration rearranges to a more stable boron enolatelike compound 9 (Scheme 2), in a manner similar to that which occurs in reactions of trialkylboranes with anions of α-bromocarbonyl compounds [33,34], as we have experienced previously in a phenylsulfoxide system [24]. The product of the rearrangement 9 would no longer be of the type that is susceptible to B-C migrations.…”

“…We have been extensively involved in the development of useful synthetic methods that utilize boron and lithium intermediates [22][23][24][25][26][27][28][29][30][31]. We therefore turned our attention towards reactions between trialkylboranes and appropriate lithiated 1,3-dithiane oxides derived from 1, including trans-1,3-dithiane-1,3-dioxide 2, a mixture of cisand trans-2-chloro-1,3-dithiane-1,3-dioxides 3, and 2-substituted 1,3-dithiane-1-oxides 4-6 (Figure 1).…”

Studies on a catalytic version of the Matteson asymmetric homologation reaction

“…25 However, the process needed a significant (five-fold) excess of the chiral ligand in order to provide a good level of asymmetric induction in the reaction studied, ostensibly because lithium chloride generated in situ competed for the ligand. 25 As part of our interest in the use of organometallic intermediates and in particular boron reagents in organic syntheses, [26][27][28][29][30][31][32] we decided to investigate this procedure in more detail in the hope that we may be able to overcome the difficulties and develop a procedure that was successful with a much smaller quantity of chiral ligand. We now report our results.…”