Double Aldol Research Articles

Boron-Mediated Double Aldol Reaction of Carboxylic Esters

Boron-Mediated Double Aldol Reaction of Carboxylic Esters

ChemInform Abstract: Stereospecific Double Aldol Reaction of Phenylacetaldehyde Catalyzed by Group 4 Metallocene.

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Stereospecific Double Aldol Reaction of Phenylacetaldehyde Catalyzed by Group 4 Metallocene

Abstract Reaction of phenylacetaldehyde with catalytic amount of “Cp2M” (M = Ti, Zr) produces spectroscopically pure 5-benzyl-1, 3-dihydroxy-2, 4-diphenyl pyran as single isomer in good yield, which could be assumed formal trimerization of phenylacetaldehyde.

Enantiomerically pure sulphinyl-4,5-dihydroisoxazoles. Part 2. Synthesis of masked and unmasked β,β′-dihydroxy ketones via stereocontrolled double aldol condensation

Reaction of stereoisomerically pure sulphinyl-4,5-dihydroisoxazoles having one or two stereocentres at C-4 and C-5 of the heterocycle with aliphatic or aromatic aldehydes resulted in highly stereoselective formal double aldol condensation; the adducts, depending on desulphurization conditions, could be converted either into optically active ββ′-dihydroxy ketones (by Raney nickel catalyzed hydrogenation in the presence of boric acid) or hydroxyisoxazolines (by Na-Hg in buffered conditions); the latter have the heterocyclic ring available for further synthetic elaboration such as highly stereoselective lithium aluminium hydride reduction to amino diols.

ChemInform Abstract: CONSTRUCTION OF HIGHLY SUBSTITUTED NITROAROMATIC SYSTEMS BY CYCLOCONDENSATION. PART II. CONVERSION OF 4‐NITRO‐3‐OXOBUTYRATE TO 3‐NITROSALICYLATES

AbstractDie Titelverbindung (I) reagiert mit einer Reihe von Ketoverbindungen wie (II), (IV), (VIII) und (XI) unter Ringschluß zu den 3‐Nitrosalicylaten (III), (V)‐(VII), (IX), (X), (XII) und (XIII).

Double aldol condensation: stereoselective synthesis of masked and un-masked β,β′-dihydroxyketones

Aldol condensations of stereoisomerically pure 3-sulphinylmethyl-4-5-dihydroisoxazoles allow a highly stereocontrolled entry to optically active masked and un-masked β,β′-dihydroxyketones.

Construction of Highly Substituted Nitroaromatic Systems by Cyclocondensation. Part II. Conversion of 4‐nitro‐3‐oxobutyrate to 3‐nitrosalicylates

AbstractThe base‐catalyzed reaction of 4‐nitro‐3‐oxobutyrate (6) with acetylacetone (8 Scheme 3), formylacetone (13, Scheme 4), formylcyclohexanone (31, Scheme 5), 2,4‐dioxopentanoates 39 and 40 (Scheme 6), and 2,4,6‐heptanetrione (2, Scheme 7) affords substituted 3‐nitrosalicylates, products of a double aldol condensation. With unsymmetrical dicarbonyl compounds both regioisomers are formed. High selectivity was found in the case of β‐keto‐aldehydes 13 and 31 with preferred addition of the NO2‐substituted carbon to the aldehyde carbonyl. The major products of these cyclocon‐densations, which are isolated in yields ranging from 20% to 80%, are all new compounds. Less successful are the conversions with β‐alkoxy‐ and β‐chloro‐vinyl ketones (23, 25, and 26), and with alkinone 24, where the condensation products are formed in very low yield (Scheme 4).

Total synthesis of dl-19-nor-16,17-dehydroprogesterone.

dl-2-(7,11-Dimethyl-3,7,11 - trans,trans-dodecatrienyl)-3-methyl-cyclopent-2-enol was prepared by reduction of the corresponding ketone. This tetraenol, on treatment with trifluoroacetic acid, underwent stereoselective cyclization to give dl-3,17-dimethyl-A-nor-D-homoestra-3,16-diene. This tetracyclic material was readily converted, by oxidative cleavage to the bicyclic triketo aldehyde followed by a double aldol cyclization, into dl-19-nor-16,17-dehydroprogesterone.