Aldol Reactions Of Methyl Ketones Research Articles

The Influence of a β-Electron Withdrawing Substituent in Aldol Reactions of Methylketone Boron Enolates

We wish to describe here that good levels of substrate-based, 1,5-syn-stereocontrol could be achieved in the boron-mediated aldol reactions of beta-trichloromethyl methylketones with achiral aldehydes, independent of the nature of the beta-alkoxy protecting group.

Regiospecific Organocatalytic Asymmetric Aldol Reaction of Methyl Ketones and α,β‐Unsaturated Trifluoromethyl Ketones.

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Regiospecific Organocatalytic Asymmetric Aldol Reaction of Methyl Ketones and α,β-Unsaturated Trifluoromethyl Ketones

[structure: see text]. The aldol reaction of methyl ketones and alpha,beta-unsaturated trifluoromethyl ketones occurred under mild conditions with the combination of proline-derived N-sulfonylamide and trifluoroacetic acid as the catalyst to give the corresponding unsaturated alpha-trifluoromethyl tertiary alcohols in high yields with good enatioselectivities.

Enantioselectivity in the boron aldol reactions of methyl ketones

DFT computed transition states quantitatively explain the surprising stereochemical outcome of unsubstituted enolborinates in diastereoselective and enantioselective boron aldol reactions.

Synthesis of the C11-C29 fragment of amphidinolide F.

[reaction: see text] An efficient synthesis of the C(11)-C(29) fragment 31 of amphidinolide F has been accomplished via a diastereoselective [3 + 2]-annulation reaction of allylsilane 5 and ethyl glyoxylate to prepare the key tetrahydrofuran 15 and a highly stereoselective methyl ketone aldol reaction to generate the C(11)-C(16) segment.

High 1,5‐anti Stereoinduction in Boron‐Mediated Aldol Reactions of Methyl Ketones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

High 1,5-anti stereoinduction in boron-mediated aldol reactions of methyl ketones.

[reaction: see text] We report herein a very efficient and synthetically useful 1,4-anti-1,5-anti boron-mediated aldol reaction of a chiral alpha-methyl-beta-alkoxy methyl ketone with achiral aldehydes.

An NMR method for assigning relative stereochemistry to beta-hydroxy ketones deriving from aldol reactions of methyl ketones.

We describe a simple 1H NMR analysis that permits the stereochemistry of beta-hydroxy ketones to be assigned by visual inspection of the ABX patterns for the alpha-methylene unit of the beta-hydroxy ketone in the 1H NMR spectra. This method has been verified by application to a wide range of beta-hydroxy ketones deriving from aldol reactions of chiral aldehydes with a variety of chiral and achiral methyl ketone enolates (see Tables 1 and 2). The stereochemistry of 54 of these compounds have been assigned by rigorous chemical methods.

Remote 1,5-stereoinduction in boron aldol reactions of methyl ketones: application to the convergent assembly of the 1,3-polyol sequence of (+)-roxaticin

By exploiting 1,5-anti stereoinduction in the boron aldol coupling of the β-alkoxy methyl ketones 6 and 8 with aldehydes 7 and 9, the convergent synthesis of 2, corresponding to the fully protected polyol sequence of the 30-membered macrolide, (+)-roxaticin (1), was achieved in an efficient manner (15 steps and 24.0% yield from ketone 15).

Enantioselective total synthesis of altohyrtin C (spongistatin 2)

The first total synthesis of a spongipyran macrolide, altohyrtin C, is described. The convergent synthesis strategy relies on a regioselective macrolactonization, a stereoselective Wittig coupling of the two major synthetic fragments, a complex anti aldol reaction to join the C 1–C 15 and C 16–C 28 spiroketal regions, and an anomeric sulfone acylation to join the C 29–C 37 and C 38–C 43 pyran regions. The incorporation of the C 44–C 51 sidechain in the final stages of the synthesis establishes a viable route for the construction of variants in this pharmacologically important region. Methodological developments en route to the total synthesis include a 1,5 anti-selective methyl ketone aldol reaction and a diastereoselective approach to Lewis acid mediated β- C-glycosidation. Completion of the synthesis has confirmed the stereochemical assignments proposed in the altohyrtin series and has established the identity of the altohyrtin and spongistatin marine macrolides.

Studies of fragment assembly aldol reactions of chiral aldehydes and chiral methyl ketones: stereoselective synthesis of the C(13)–C(25) segment of scytophycin C

Abstract A highly stereoselective synthesis of the C(13)–C(25) fragment of scytophycin C is described, along with stereochemical studies of the key fragment assembly methyl ketone aldol reaction.

Total Synthesis of (-)-Bafilomycin A1 : Application of Diastereoselective Crotylboration and Methyl Ketone Aldol Reactions.

A careful orchestration of protecting groups is an essential requirement for the total synthesis of the macrolide antibiotic bafilomycin A1 (1). Key steps were the Suzuki cross-coupling reaction of two advanced, suitably protected intermediates prior to closure of the macrocycle, as well as a highly stereoselective methyl ketone aldol reaction.

Mechanistic insights from ab initio calculations on a nitrogen analogue of the boron-mediated aldol reaction

Molecular orbital calculations were used to study a nitrogen analogue of the boron mediated aldol reaction. Experimental results show that high selectivity can be obtained in some cases, at the cost of low yields. The molecular orbital calculations are used to analyse the experimental results and to suggest modifications to the experimental procedure. The results suggest an explanation for a puzzling reversal of selectivity in the aldol reactions of methyl ketones.

Enantio- and diastereoselective aldol reactions of achiral ethyl and methyl ketones with aldehydes: the use of enol diisopinocampheylborinates

Enol diisopinocampheylborinates, derived from achiral ethyl and methyl ketones by enolisation in the presence of tertiary amine bases ( iPr 2NEt or Et 3N), undergo enantio- and diastereoselective aldol reactions with aldehydes. The reagents employed, (+)- and (-)-(Ipc) 2BOTf, are easily prepared in enantiomerically pure form in two steps from (-)- and (+)-α-pinene, respectively. The aldol reaction between ethyl ketones and aldehydes using (+)- or (-)- (Ipc) 2BOTf/ iPr 2NEt in dichloromethane gives, via the derived chiral Z-enol borinates, syn-α-methyl-β-hydroxy ketones in good enantiomeric excess (66-93% ee) and with high diastereoselectivity (>-95%). In contrast, the anti-selective aldol reaction of diethylketone via the isomeric E-enol diisopinocampheylborinate (by enolisation with (-)-(Ipc) 2BCl) with methacrolein proceeds with negligible enantioselectivity. Use of both the triflate and chloride reagents in the aldol reaction of methyl ketones with aldehydes gives β-hydroxy ketones in moderate enantiomeric excess (53–78% ee) with a reversal in the enantioface selectivity of the aldehyde compared to the corresponding ethyl ketone syn aldol. This variable selectivity is interpreted as evidence for the participation of competing chair and boat transition states. Other chiral dialkylboron triflate reagents investigated led to reduced enantioselectivities in diethylketone-aldehyde aldol reactions.

Reversal of aldehyde diastereofacial selectivity in a methyl ketone aldol reaction. Application to the synthesis of the calyculin spiroketal

It has been observed that aldehyde diastereofacial selectivity in a methyl ketone aldol reaction can be fully regulated under appropriate conditions. Addition of the lithium enolate provided the product derived from apparent chelation control, while Lewis acid-promoted addition of the derived silyl enol ether afforded the Felkin-Anh diastereomer. Application of this methodology to the ongoing synthesis of calysulin A is presented.

ChemInform Abstract: Aldol Reactions of Methyl Ketones Using Chiral Boron Reagents: A Reversal in Aldehyde Enantioface Selectivity.

AbstractAcetone (I) and its substituted derivatives (IV) are subjected to selective enolization with a chiral borinate in the presence of di(isopropyl)ethylamine and subsequent coupling with the aldehydes (II), yielding the hydroxy ketones (+)‐(III) or (+)‐(V) as the main products.

Aldol reactions in polypropionate synthesis: High π-face selectivity of enol borinates from α-chiral methyl and ethyl ketones under substrate control

Use of ( c-C 6H 11) 2BCl in the anti-selective aldol reaction of the α-chiral ethylketone 2 leads to high stereoselectivity (>94%) for the 1,2- anti-2,4- anti isomer 7. The related α-chiral methylketone aldol reaction, 8 → 9, proceeds with 84–93% diasteroselectivity for a range of boron reagents.

Regiospecific directed aldol reactions of methyl ketones with aldehydes

Regiospecific directed aldol reactions of methyl ketones with aldehydes