(Z)-Selective Takai olefination of salicylaldehydes

Abstract

The Takai olefination (or Takai reaction) is a method for the conversion of aldehydes to vinyl iodides, and has seen widespread implementation in organic synthesis. The reaction is usually noted for its high (E)-selectivity; however, herein we report the highly (Z)-selective Takai olefination of salicylaldehyde derivatives. Systematic screening of related substrates led to the identification of key factors responsible for this surprising inversion of selectivity, and enabled the development of a modified mechanistic model to rationalise these observations.

Chromium-catalyzed olefination of arylaldehydes with haloforms assisted by 2,3,5,6-tetramethyl-N,N′-bis(trimethylsilyl)-1,4-dihydropyrazine

“…It is noteworthy that the opposite trans / cis selectivity was observed for ortho -disubstituted arylaldehydes, 2,6-dimethoxybenzaldehyde ( 2w ) and 2,4,6-trimethoxy-substituted ( 2x ), while keeping the high yields of the products 3w,x , suggesting that the methoxy group at the ortho -position served as a directing group to the chromium center to increase the cis -isomers. 11 In fact, these results were different from the olefination without 1a under Takai's olefination conditions: the same substrate combination of 2x and CHBr 3 in the presence of excess amounts of CrCl 2 afforded the corresponding trans -β-chloroalkene 3x′ as the major product (29%, trans : cis = 76 : 24) together with co-production of 3x in 19% yield ( trans : cis = 68 : 32) (see ESI†). In addition, the carbonyl olefination of 4,4′-diformylbiphenyl ( 2y ) gave 3y in 47% yield by increasing the reagents to the double amounts.…”

Unveiling the Takai Olefination Reagent via Tris(tert-butoxy)siloxy Variants

“…However, it has been hypothesized that the active species is either a chromium dihalido-methanide species (Scheme , A ) or more favorably the ostensible dichromium monohalido-methylidene (Scheme , B ). This uncertainty has been extensively studied over the years, − substantiating species B as the likely candidate. Yet, as neither type ( A or B ) has ever been isolated, both must still be considered as the active species, especially as metal-halido-methanide complexes can initiate the olefination of aldehydes .…”

Toward the Rational Design of Universal Dual Polarity Matrix for MALDI Mass Spectrometry

“…Based on these criteria and the dual acid–base functionality, we strategically designed and synthesized a series of new MALDI matrices I – IV (see Scheme ) containing a simple aniline derivative anchored by a carboxyl group for COOH-NH 2 ( I ) and COOH-NHMe ( IV ), and formyl group for CHO-NH 2 ( II) , and CHO-NHAc (III) . Though I – IV have been synthesized previously, their related application as a MALDI matrix as part of a rationally designed strategy have not been proposed, especially for II – IV . − The amphoteric property of COOH-NH 2 ( I ) and COOH-NHMe ( IV ) could allow the detection of both positive and negative ions in MALDI. In this study, we demonstrated that these dual polarity MALDI matrix, COOH-NH 2 ( I ) and COOH-NHMe ( IV ), allowed complementary analysis of lipids and proteins, including the positively charged and negatively charged species, within one experiment.…”