Synthesis of allyltitanium compounds by intramolecular nucleophilic acyl substitution reaction of alka-3,5-dienyl carbonates and their unusual regioselectivity in reaction with aldehydes

Abstract

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Efficient and Practical Method for Synthesizing N-Heterocyclic Compounds Using Intramolecular Nucleophilic Acyl Substitution Reactions Mediated by Ti(O-i-Pr)4/2i-PrMgX Reagent. Synthesis of Quinolones, Pyrroles, Indoles, and Optically Active N-Heterocycles Including Allopumiliotoxin Alkaloid 267A

“…On the other hand, the N-crotylated substrate 4b which has the disubstituted double bond did not afford the corresponding INAS-ICA product. This may be due to steric hindrance as was observed in the reaction of 1 with olefinic esters 3 4c. The reaction with the N-propargylated compounds 5a,b also proceeded as expected to afford the corresponding INAS reaction products 7 in good yields by the reaction with 1 ; the presence of an intermediate alkenyltitanium species before the aqueous workup of the reaction mixture was confirmed by deuterolysis (eq 2).…”

“…Recently, we have found that the reaction of Ti(O- i -Pr) 4 with 2 equiv of i -PrMgX (X = Cl or Br) provides (η 2 -propene)Ti(O- i -Pr) 2 ( 1 ) in an essentially quantitative yield and that 1 acts as a versatile titanium(II) equivalent . In the course of our studies to develop synthetic methodology based on this reagent, we have revealed that the reaction with acetylenic esters 2 results in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford organotitanium compounds having a carbonyl functional group in good to excellent yields and the Cha group also independently found that in the reaction with olefinic ester 3 , the resulting INAS products undergo intramolecular carbonyl addition (ICA) reaction to afford cyclopropanol derivatives.…”

5.34 Early Transition Metal Mediated Reductive Coupling Reactions

“…As generally depicted in Scheme 31B, Ti-p complex formation is thought to be followed by intramolecular nucleophilic attack to deliver an intermediate bicyclic product, the fate of which is dictated by the nature of the unsaturated system (alkene, alkyne, allene, or 1,3-diene), the substituents X and Y, and the ring size. [81][82][83][84][85][86] These processes have been termed, 'intramolecular nucleophilic acyl substitution' (INAS) reactions and have been explored as a means to prepare a variety of nitrogen-containing heterocycles (Scheme 32A). Recently, this type of early transition metal-mediated process has appeared as a key step in the total synthesis of allopumiliotoxin 267A (Scheme 32B).…”

Titanacyclopentene complexes and their application as 1,4-dicarbanion equivalentsElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b311572k/

“…Sato et al reported the conversion of hexa-3,5-dienyl ethyl carbonate with complex 1 and proposed a 1,4-dicarbanionic titanacyclopentene intermediate similar to structure 2b. 4 On the other hand, de Meijere et al observed that conjugated dienes and trienes were accepted by 1 as particularly good ligands, but the resulting intermediate 2 behaved selectively as a 1,2-dicarbanionic vinyltitana-cyclopropane when trapped with dibenzylformamide. 5 We now report an effective intermolecular coupling of but-3-enylmagnesium chloride with 2 equivalents of an electrophile in the presence of Ti(OiPr) 4 .…”