Captodative substituent effects — Part XXXI olefins with captodative substitution in [2+2] cycloadditions

Captodative olefins in polymer chemistry

“…Some captodative olefins homodimerize near room temperature [141,[144][145][146] and an intramolecular example is also known (Scheme 4) [t47]. These [2 +2]-cycloadditions are often reversible.…”

Total Synthesis of Meloscine by a [2+2]‐Photocycloaddition/Ring‐Expansion Route

“…As there was no precedence of any such [2 + 2]-photocycloaddition, it came as a pleasant surprise that enol ether 15 [31] derived from methyl pyruvate proved to be an excellent substrate for the planned transformation. [32] Irradiation of a toluene solution of quinolone 8 and an excess of enol ether 15 with UV light (l = 350 nm) gave the desired cisfused cyclobutane 16 as a single diastereoisomer in almost quantitative yield. Obviously, the a-silyloxy substituent of acrylate 15 and the resulting captodative electronic situation at C-a exhibit a favorable effect on the course of the [2 + 2]-photocycloaddition, as both yield and stereoselectivity surpassed the values obtained with any a-alkyl substituted acrylate investigated earlier.…”

Clean and atom-economic synthesis of alpha-phenylselenoacrylonitriles and alpha-phenylseleno- alpha,beta-unsaturated esters by knoevenagel reaction under solvent-free conditions

“…2 Special attention has been devoted to the synthesis of vinyl selenides substituted by electron-withdrawing groups, like nitriles 3 and esters 4. These highly functionalized compounds can be submitted to several transformations, including their use in [2+2] cycloaddition reactions, 3 Diels-Alder reactions, [4][5][6] and like Michael acceptors. 4,7 The α-phenylseleno-α,β-unsaturated esters 4 have been prepared by different routes, 2 including selenilation of ester enolates, 8 oxidative elimination of α,α-bis(phenylselanyl)esters, 8 dehydrochlorination of α-phenylseleno-β-chloro esters 8 and of α-phenylseleno-α-chloro esters, 9 and Wittig-type reactions.…”

“…6,10 On the other hand, the preparation of α-phenylselenoacrylonitriles 3 was studied in a minor extent. 2,3,4,11,12 Between the described methods for preparation of 3, those involving Wittig-type reactions are the most efficient. 4,12 Recently, Chinese authors have been described the preparation of several α-phenylseleno-α,β-unsaturated nitriles in moderate to good yields via α-phenylselenenyl cyanomethylene triphenylarsorane.…”

“…6 In contrast to Wittig type reactions, Knoevenagel condensation is an atom-economic and cleaner tool for constructing the α,β-unsaturated structure unit from a carbonyl and an active methylene components. 13 Knoevenagel reactions can be promoted by solid supported reagents, 14 fluoride anion, 15 and KF/Al 2 O 3 16 and the generation of large amounts of salts at the end of the synthesis as well as the use of stoichiometric strong bases can be avoided.…”