Cyclopropylamines from N,N‐Dialkylcarboxamides and Grignard Reagents in the Presence of Titanium Tetraisopropoxide or Methyltitanium Triisopropoxide

Abstract

Thirty-three different N,N-dialkyl- and N-alkyl-N-phosphorylalkyl-substituted carboxamides 9-17 were treated with unsubstituted as well as with 2-alkyl-, 2,2-dialkyl-, and 3-alkenyl-substituted ethylmagnesium bromides 6 in the presence of stoichiometric amounts of titanium tetraisopropoxide or methyltitanium triisopropoxide to furnish substituted cyclopropylamines 20-25 in 20-98% yield, depending on the substituents with no (1:1) to excellent (>25:1) diastereoselectivities. Generally higher yields (up to 98%) of the cyclopropylamines 20-28 without loss of the diastereoselectivity were obtained with methyltitanium triisopropoxide as the titanium mediator. Under these conditions, even dioxolane-protected ketones and halogen-substituted and chiral as well as achiral alkyloxyalkyl-substituted carboxamides could be converted to the correspondingly substituted cyclopropylamines with unsubstituted as well as phenyl- and a variety of alkyl-substituted ethylmagnesium bromides in addition to numerous heteroatom-containing (e.g., halogen-, trityloxy-, tetrahydropyranyloxy-substituted) Grignard reagents (62 examples altogether). The transformation of N,N-diformylalkylamines 54 with ethylmagnesium bromide in the presence of methyltitanium triisopropoxide to N,N-dicyclopropyl-N-alkylamines 55 can be brought about in up to 82% yield (6 examples). An asymmetric variant of the titanium-mediated cyclopropanation of N,N-dialkylcarboxamides has been developed by applying chiral titanium mediators generated from stoichiometric amounts of titanium tetraisopropoxide and chiral diamino or diol ligands, respectively. The most efficient chiral mediators turned out to be titanium bistaddolates that provided the corresponding cyclopropylamines with enantiomeric excesses (ee) of up to 84%. Evaluation of several silyl-based additives revealed that the reaction can also efficiently be carried out with substoichiometric amounts (down to 25 mol%) of the titanium reagent, as long as 2-aryl- or 2-ethenyl-substituted ethylmagnesium halides are used and a concomitant slight decrease in yields is accepted. The newly developed methodology was successfully applied for the preparation of analogues with cyclopropylamine moieties of known drugs and natural products such as the nicotine metabolite (S)-Cotinine as well as the insecticides Dinotefuran and Imidacloprid.

Copper-Catalyzed Regiospecific and 1,2-Regioselective Cyclopropanation of (1Z)-1-Amino- and (1Z)-1-Oxy-1,3-butadienyl Derivatives

“…The method affords the corresponding 1-amino-or 1-oxy-2-vinyl (alkenyl) cyclopropane derivatives 4, [9][10][11] which could act as an interesting building block for the synthesis of biologically active compounds. 12 First, we examined the copper(II)/acid-catalyzed cyclopropanation of (E)-and (Z)-1 with methyl p-bromophenyldiazoacetate (2a) to clarify the effects of the double-bond geometry and the 1-EDG for 3,4-vs. 1,2-regioselectivity (Table 1).…”

Chiral γ‐Lactams by Enantioselective Palladium(0)‐Catalyzed Cyclopropane Functionalizations

“…17, 18 Herein, we report a highly enantioselective synthesis of saxagliptin‐type 2‐azabicyclo[3.1.0]hexane derivatives 2 by an asymmetric CH functionalization strategy (Scheme ). The required aminocyclopropane substrates 1 are conveniently accessed by Kulinkovich–Szymoniak19 or Kulinkovich–de Meijere reactions 20. The chloroacetamide group of 1 serves as the alkyl electrophile required to access the alkyl palladium intermediate A .…”

From Dialkyltitanium Species to Titanacyclopropanes: An Ab Initio Study

“…Despite its wide use in synthesis, the mechanism of formation of the dialkoxytitana­cyclopropane intermediate A is not really understood as demonstrated by the diverse names used in the literature for this transformation: β-hydride transfer, β-hydride elimination, disproportionation, β-hydrogen abstraction, β-fragmentation, epimetalation, etc.…”