1,3‐Bis(dimethylamino)vinylcarbene

Abstract

oil) and (22b) (36 %, orange-red oil) with dimethylamine.HBF4 regenerates (23) also obtained instead of ( 9 ) on treatment of ( 8 b ) and ( 8 k ) with an excess of dimethylamine. ( 2 4 ) (72%) and ( 2 5 ) are suitable precursors for donor-substituted cyclopentadienylium salts and cyclopentadienones. ( 9 d ) , 61151-51-9; (9e), 61151-59-1; (Sf), 67151-61-5; ( 9 g ) , 61151-63-1; (9h). 61150-11-4; ( 9 i ) , 61150-13-6; (9j), 61750-75-8; ( 9 n ) . 61161-61-9; (l0a),61150-16-9; ~lOb),61150-11-0; ( l l a ) , 61750-18-1; ( l l b ) , 61150-19-2; ( l 2 ) , 61150-80-5; ( 1 3 a ) , 61750-82-1; ( 1 3 h ) , 61750-84-9; ( 1 3 c ) , 61150-86-1; (13d), 61150-88-3 1,3-Bis(dimethylarnino)vinylcarbene[ By Rudolf Gompper and Ruiner Sobottu"]In compliance with the charge distribution in the ally1 system, I-acceptor substituted vinamidinium salts (1) preferentially react with nucleophiles at C-3"'. However, the ambifunctional character of ( 1 ) also embraces the acceptor groupA: treatment of (1 a ) with Na ethoxide in ethanol leads exclusively to the salt ( 4 ) together with ethyl benzoate. The simplest explanation of this behavior invokes the intermediacy of the nucleophilic carbene ( 3 ) , which undergoes subsequent protonation. Analogous eliminations of acyl groups have been observed with 2-acyl-I -methylpyridinium saltsf3]; the decarboxylation of l-methylpyridinium-2-carboxylatef41 should also be mentioned in this context. A detailed study of the reactions of the nucleophilic vinylcarbene (3) is facilitated by the possibility of generating the species from the zwitterion (2), which is accessible by alkaline hydrolysis of ( I b ) (81 %; colorless crystals; see Scheme 1).Heating of (2) with an excess of benzoyl chloride or 4-chlorobenzoyl chloride to 160°C affords ( 1 a), or ( 5 ) , respectively, in 65-70 0 4 yield. Similar reaction with benzaldehyde gives the furan ( 6 ) .The reaction of (2) with tetraethyl allenetetracarboxylate, leading to the zwitterion (7) (32 %; yellow needles), is remarkable. The formation of (7) demonstrates that cyclopropanes do not necessarily result on reaction of carbenes with olefins (for further examples, see ref.[51).

Diels−Alder Reactions of 4-Alkenylthiazoles: A New Approach to Thiazole Functionalization

“…The reactivity of dienes increases not only with the number of electron-releasing substituents but also when they are placed in adequate positions to cause a cooperative effect. Thus, the Danishefsky−Kitahara and Rawal dienes, with electron-donor substituents at 1- and 3-positions, display high reactivity in [4 + 2] cycloaddition reactions. − The enhanced reactivity of both dienes has been rationalized on the basis of FMO theory, which also afforded accurate semiquantitative predictions of the behavior of other dienes and dienophiles in [4 + 2] cycloadditions . We have also used this methodology for investigating the relative reactivity of dienes 1f − j (Chart ), and here we compare the results with those obtained for Danishefsky−Kitahara ( 5 in Chart ) and Rawal dienes computed at the same level of theory.…”

On the Reactivity of 1-Amino-3-siloxy-1,3-dienes: Kinetics Investigation and Theoretical Interpretation

“…This perturbation decreases the energy difference between the diene HOMO and the dienophile LUMO, consonant with greater stabilization of the transition state and reflected in a higher reaction rate . Activation of the diene increases as electron-donating substituents are incorporated into the diene structure, ideally at 1- and 3-positions, which causes a cooperative increase in reactivity. − …”