Chiral synthesis via organoboranes. 24. B-allylbis(2-isocaranyl)borane as a superior reagent for the asymmetric allylboration of aldehydes

Brown, Herbert C.; Randad, Ramnarayan S.; Bhat, K. S.; Zaidlewicz, M.; Racherla, Uday S.

doi:10.1021/ja00162a047

Cited by 132 publications

(44 citation statements)

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“…The calculated (DFT/PBE/L1) geometry of each of the four possible epimers of 16a was used to evaluate the 3 J(H,H) by the Karplus equation [22]. The characteristic calculated and corresponding experimental 3 J(H,H) provided evidence for the ct epimer as the most reliable one, while tc and tt did not agree with the experimental data at all.…”

Section: Configuration Of Compoundsmentioning

confidence: 99%

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

Ильина

Волчо

Корчагина

et al. 2010

Helvetica Chimica Acta

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The reactions of (þ)-car-2-ene (1) and (þ)-car-3-ene (2) with aldehydes in the presence of montmorillonite clay were studied for the first time (Schemes 3 and 5). The major products of these reactions are optically active, substituted hexahydroisobenzofurans, probably formed as a result of an attack of the protonated aldehyde at the cyclopropane ring. Quite unexpectedly, the products are cisconfigured at the ring-fusion site; the fact was established by means of quantum-chemical calculations and NMR data. It appeared that the behavior of the 2 : 3 mixture 1/2 in reactions with aldehydes in the presence of K10 clay differed substantially from the reactivities of the corresponding individual monoterpenes.

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Section: Configuration Of Compoundsmentioning

confidence: 99%

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

Ильина

Волчо

Корчагина

et al. 2010

Helvetica Chimica Acta

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“…Due to the close position of the newly formed asymmetric centers to the cyclopropane ring, the chiral b-amino acids obtained in these reactions are promising compounds for further use in asymmetric synthesis. Indeed, as is known, the chiral ligands obtained from (þ)-car-2-ene exceed by far (in asymmetric induction) the analogous ligands obtained from (þ)-car-3-ene or a-pinene in syntheses of syn-aldols [16] and asymmetric allylboration [17].…”

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confidence: 91%

Synthesis of Derivatives of the Optically Active β‐Amino Acids from (+)‐Car‐2‐ene

Koneva

Волчо

Gatilov

et al. 2008

Helvetica Chimica Acta

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The reaction of (þ)-car-2-ene (4) with chlorosulfonyl isocyanate (¼ sulfuryl chloride isocyanate; ClSO 2 NCO) led to the tricyclic lactams 6 and 8 corresponding to the initial formation both of the tertiary carbenium and a-cyclopropylcarbenium ions (Scheme 2). A number of optically active derivatives of bamino acids which are promising compounds for further use in asymmetric synthesis were synthesized from the lactams (see 16, 17, and 19 -21 in Scheme 3). As is known [10] [11], the reaction of (þ)-car-3-ene (1) with CSI leads to the formation of compound 2 (Scheme 1), and reductive treatment of the latter furnishes bicyclic lactam 3 with a total yield of up to 76% after both steps. Methanolysis of 3 is possible after activation of the lactam group with the (tert-butoxy)carbonyl group [11], or by using silica chloride as a catalyst, which can be prepared by the interaction of silica gel with SOCl 2 [12] (Scheme 1). At the same time, no data are currently available on the interaction of CSI with (þ)-car-2-ene (4), which generally differs widely from (þ)-car-3-ene (1) in its reactivity in reactions with electrophiles. The aim of the present work was the synthesis of derivatives of the optically active b-amino acids derived from commercially available (þ)-car-2-ene (4).

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“…5 Previously, we had reported the synthesis of compound 9, where the intermediate 8 was synthesized from 7 using Brown's B-allyl bis(4-isocaranyl)borane in 92% ee. 6,7 However, for the preparation of ent-8, we found Leighton's allyl silane reagent 10 8 to be operationally more practical, and also provided slightly better ee in comparison to B-allyl bis(2-isocaranyl)borane. 9,10 From ent-8 (92% ee), 11 the cis-substituted tetrahydropyran ent-5 was prepared according to the synthesis of 5.…”

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confidence: 93%

Synthesis of Spirastrellolide A Fragments for Structure Elucidation

Pan¹,

Brabander²

2006

Synlett

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A stereocontrolled synthesis of two diastereomeric C 1 -C 22 fragments of spirastrellolide A consistent with reported spectroscopic data has been achieved to aid in a complete configurational assignment of this structurally novel and potent antimitotic natural product. A highly convergent coupling of two enantiomeric C 1 -C 10 methyl ketone fragments with an enantiopure C 11 -C 22 spiroketal aldehyde produced the C 1 -C 22 fragments with a longest linear sequence of 13 steps from commercially available starting materials.Given our fascination with structurally novel bioactive natural products, we became interested in spirastrellolide A -a potent antimitotic macrolactone isolated from extracts of a Caribbean marine sponge by Andersen and coworkers. 1 A revised and more complete structure of spirastrellolide A was reported in a subsequent manuscript, which also included data related to its ability to potently inhibit protein phosphatase 2A (PP2A). 2 Although the relative stereochemistry within the C 3 -C 7 (cis) and the C 9 -C 24 fragments has been elucidated, the relative stereochemistry between these fragments remains uncertain. 2 As shown in Figure 1, we targeted two alternative C 1 -C 22 fragments 3 and 4 that represent the two diastereomers compatible with the published structural information. 3,4 These diastereomers in turn would be available through a substrate-controlled 1,3-anti Mukaiyama aldol reaction of enantiomerically pure spiroketal aldehyde 6 with the two enantiomeric cis-tetrahydropyranyl fragments 5 and ent-5, followed by a 1,3-anti-b-hydroxy ketone reduction. An added advantage of this convergent approach is that it allows for the synthesis of additional stereoisomers (C 9 , C 11 ) in the linker region connecting the cis-THP and the spiroketal fragments.The synthesis of the two enantiomeric cis-tetrahydropyranyl fragments 5 and ent-5 is shown in Scheme 1, and is based on a final Wacker oxidation of allyl-substituted tetrahydropyranyl derivative 9 to yield methyl ketone 5 in 70% yield. 5 Previously, we had reported the synthesis of compound 9, where the intermediate 8 was synthesized from 7 using Brown's B-allyl bis(4-isocaranyl)borane in 92% ee. 6,7 However, for the preparation of ent-8, we found Leighton's allyl silane reagent 10 8 to be operationally more practical, and also provided slightly better ee in comparison to B-allyl bis(2-isocaranyl)borane. 9,10 From ent-8 (92% ee), 11 the cis-substituted tetrahydropyran ent-5 was prepared according to the synthesis of 5.

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Chiral synthesis via organoboranes. 24. B-allylbis(2-isocaranyl)borane as a superior reagent for the asymmetric allylboration of aldehydes

Cited by 132 publications

References 0 publications

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

Unusual Reactions of (+)‐Car‐2‐ene and (+)‐Car‐3‐ene with Aldehydes on K10 Clay

Synthesis of Derivatives of the Optically Active β‐Amino Acids from (+)‐Car‐2‐ene

Synthesis of Spirastrellolide A Fragments for Structure Elucidation

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