Enantioselective michael-mukaiyama additions of silylketene acetals to 2-carboxycyclopentenones promoted by chiral Ti complexes

Bernardi, Anna; Karamfilova, K.; Boschin, Giovanna; Scolastico, Carlo

doi:10.1016/0040-4039(94)02478-t

Cited by 25 publications

(4 citation statements)

References 16 publications

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“…A complementary chiral auxiliary based on phenylglycinol gave nearly as good results . Other chiral auxiliaries include one 684 derived from proline, which can be attached to cyclohexenones (Scheme ), another derived from camphor, which has been used as part of the catalyst in a reaction of silyl nitronates, another derived from BINAP used on open-chain enones, and another (TADDOL) derived from tartaric acid, which has been used in a reaction on cyclopentenones 167 …”

Section: Intermolecular Attack On Enonesmentioning

confidence: 99%

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

1997

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Section: Intermolecular Attack On Enonesmentioning

confidence: 99%

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

1997

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“…For instance, addition of Me,SiCN to aldehydes [28], for Diels-Alder additions [29-3 I], for hetero-Diels-Alder reactions (Si-enolether + nitroolefins [32]), and R,Zn additions to nitrostyrenes [33], Michael additions [34], and for iodolactonizations [35]. Useful catalytic applications not referred to in the reviews [ S ] [6] are for instance Diels-Alder reactions of sulfonyl-enones [36], and of keto-enones [37], cyclopropanations [38], R,Zn additions [39], and borane reductions of ketones [40].…”

Section: Applications Of Polymermentioning

confidence: 99%

“…Somewhat lower yields and selectivities were observed with the Zn-free reagents RTi(OCHMe,),, as compared to the homogeneous conditions (products 42 and 45, Scheme 5, b and c, and Table I ) . The results obtained with the dendritic TADDOLs are also included in Table I ; the yields are generally lower, with unchanged selectivities: the ligands 28-31 are separated from the poducts by chromatographic '") For instance, nucleophilic additions of alkyl, allyl, enolate, and hydride to aldehydes [ [34], and for iodolactonizations [35]. Useful catalytic applications not referred to in the reviews [ S ] [6] are for instance Diels-Alder reactions of sulfonyl-enones [36], and of keto-enones [37], cyclopropanations [38], R,Zn additions [39], and borane reductions of ketones [40].…”

Section: Applications Of Polymer-bound Taddolate Complexes For Enantimentioning

confidence: 99%

Polymer‐ and Dendrimer‐Bound Ti‐TADDOLates in Catalytic (and Stoichiometric) Enantioselective Reactions: Are pentacoordinate cationic Ti complexes the catalytically active species?

Seebàch¹,

Martí

Hintermann

1996

Helvetica Chimica Acta

230

143

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ct,rx,a',a'-Tetraaryl-l,3-dioxolane-4,5-dimethanols (TADDOLs), containing styryl groups either at C(2) of the heterocyclic ring or in the a-position, were prepared in the usual way (18-22,24,25). These compounds were copolymerized with styrene and divinylbenzene in a suspension, yielding polymers (3340, Scheme 3) as beads with a rather uniform particle-size distribution (1 5 M 5 0 pm), swellable in common organic solvents. HOCH,-and BrCH,-substituted TADDOLs were also prepared and used for attachement to Merrtfield resin or to dendritic molecules (23, 2632). The TADDOL moieties in these materials are accessible to form Ti (and Al) complexes (Scheme 4 ) which can be used as polymer-or dendrimer-bound reagents (stoichiometric) or Lewis acids (catalytic). The reactions studied with these new chiral auxiliaries are: enantioselective nucleophilic additions to aldehydes (of R,Zn and RTi(OCHMe,),; Scheme 5, Table I) and to ketones (of LiAIH,, Table 2); enantioselective ring opening of meso-anhydrides (Scheme 6); [4+2] and [3+2] cycloadditions of 3-crotonyl-1,3-oxazolidin-2-one to cyclopentadiene and to (Z)-N-benzylidenephenylamine N-oxide (4 48,49, Scheme 7, Tables 3, 4, and Fig. 5). The enantioselectivities reached with most of the polymer-bound or dendritic TADDOL Iigands were comparable or identical to those observed with the soluble analogs. The activity of the polymer-bound Lewis acids was only slightly reduced as compared with that encountered under homogeneous conditions. Multiple use of the beads (up to 10 times), without decreased performance, has been demonstrated (Figs. 3 and 4). The poorer selectivity in the Diels-Alder reaction (Scheme 7a), induced by the polymer-bound C1,Ti-TADDOLate as compared to the soluble one, is taken as an opportunity to discuss the mechanism of this Lewis-acid catalysis, and to propose a cationic, trigonal-bipyramidal complex as the catalytically active species (Fig. 6 ) . It is suggested that similar cations may be involved in other Ti-TADDOLate-mediated reactions as well.

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“…Bernardi et al (1996) reported that the adduct 6 was transformed to the known mandelate to establish the absolute configuration, although we found no data and descriptions to prove the absolute configuration of the mandelate derivative in any related literature. According to the described reference (Bernardi et al, 1995), the absolute configuration of 6 prepared by enantioselective syntheses using chiral Ti complexes was only assumed by the analogy with that found for the similar compound prepared in the same synthetic method. We deduced that insufficient verification may result in incorrect assignment of the absolute configuration of the adduct 6 in Bernardi et al (1996).…”

Section: Resultsmentioning

confidence: 99%

The Absolute Configuration of Chrysomelidial: A Widely Distributed Defensive Component Among Oribotririid Mites (Acari: Oribatida)

et al. 2012

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The absolute configuration of the iridoid monoterpene chrysomelidial from the oribatid mite, Austrotritia dentate Aoki, was elucidated by the GC-MS and GC comparisons with four synthetic stereoisomers of this well-known natural product. This identification was made possible by asymmetric synthesis of the known alcohol, (5S,8S)-chrysomelidiol. The GC retention time of diol derived from the natural oribatid dial agreed with that of the synthetic (5S,8S)-chrysomelidiol, confirming that the absolute configurations at C5 and C8 positions of the natural chrysomelidial are both S. Chrysomelidial was detected as a single or a major component in nine oribatid mites examined; thus, this compound is considered to be commonly distributed in Oribotririidae where it serves a defensive role.

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Enantioselective michael-mukaiyama additions of silylketene acetals to 2-carboxycyclopentenones promoted by chiral Ti complexes

Cited by 25 publications

References 16 publications

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

Polymer‐ and Dendrimer‐Bound Ti‐TADDOLates in Catalytic (and Stoichiometric) Enantioselective Reactions: Are pentacoordinate cationic Ti complexes the catalytically active species?

The Absolute Configuration of Chrysomelidial: A Widely Distributed Defensive Component Among Oribotririid Mites (Acari: Oribatida)

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