Competition between Hetero-Diels-Alder and Cheletropic Additions of Sulfur Dioxide to 2-Substituted Buta-1,3-dienes. Synthesis of 2-(1-Naphthyl)- and 2-(2-Naphthyl)buta-1,3-diene

Abstract

Chloroprene ( 2-chlorobuta-1,3-diene; 4b) and electron-rich dienes such as 2-methoxy-(4c), 2-acetoxy-(4d), and 2-(phenylseleno)buta-1,3-diene (4e) refused to equilibrate with the corresponding sultines 5 or 6 between À 80 and À 108 in the presence of excess SO 2 and an acidic promoter. Isoprene (4a) and 2-(triethylsilyl)-(4f), 2-phenyl-(4g), and 2-(2-naphthyl)buta-1,3-diene (4i) underwent the hetero-Diels-Alder additions with SO 2 at low temperature. In contrast, 2-(1-naphthyl)buta-1,2-diene (4h) did not. With dienes 4a, 4g, and 4i, the heteroDiels-Alder additions with SO 2 gave the corresponding 4-substituted sultine 5 with high regioselectivity. In the case of 4g SO 2 >5g, the energy barrier for isomerization of 5g to 5-phenylsultine (6g) was similar to that of the cheletropic addition of 4g to give 3-phenylsulfolene (7g). The hetero-Diels-Alder addition of 4f gave a 1 : 4 mixture of the 4-(triethylsilyl)sultine (5f) and 5-(triethylsilyl)sultine (6f). The preparation of the two new dienes 4h and 4i is reported. Introduction. ± In the two preceding reports [1] [2], we have demonstrated that the competition between hetero-Diels-Alder and cheletropic additions of sulfur dioxide depends strongly on the nature of the conjugated dienes. At low temperature (À 808) and in the presence of an acidic promoter, SO 2 adds to (E)-1-alkylbuta-1,3-diene (E)-1a giving, in agreement with the endo Alder rule [2], the corresponding cis-6-alkyl-2,6-dihydro-1,2-oxathiin 2-oxides (cis-sultines c-2a), which then equilibrate with their more stable trans-isomers (trans-sultines t-2a) (Scheme 1).

New Organic Chemistry of Sulfur Dioxide

“…This led us to investigate the factors affecting the competition between the hetero-Diels–Alder and the cheletropic addition of SO 2 . – Our studies have been reviewed. – Apart from sultines resulting from reactions of SO 2 with 1-fluoro-1,3-dienes, sultines are less stable than their sulfolene isomers. They decompose into the corresponding 1,3-dienes and SO 2 above −50 °C. – With 1-alkoxy- and 1-silyloxy-1,3-dienes 9 , the sultines 10 are not seen at −100 °C because these dienes generate the corresponding sulfolenes 11 at this temperature . Nevertheless, sultines 10 are believed to be formed before the sulfolenes.…”

“…They decompose into the corresponding 1,3-dienes and SO 2 above -50 °C. [23][24][25] With 1-alkoxy-and 1-silyloxy-1,3-dienes 9, the sultines 10 are not seen at -100 °C because these dienes generate the corresponding sulfolenes 11 at this temperature. 26 Nevertheless, sultines 10 are believed to be formed before the sulfolenes.…”

Gold(I)-Catalyzed Isomerization of Allenyl Carbinol Esters: An Efficient Access to Functionalized 1,3-Butadien-2-ol Esters

“…Functionalized 1,3-butadien-2-ol esters are attractive building blocks in organic synthesis. They have been sucessfully employed in a range of transformations mostly as diene units for inter- or intramolecular Diels−Alder reactions but also in [4+1] cycloadditions, in metal-catalyzed addition reactions, and in stereoselective hydrogenation reactions for the synthesis of chiral allylic esters . Surprisingly, there are only a few methods to access such dienes and most of them use enones as starting material and involve either high temperature 6 or strong basic 7 or acidic conditions 8 which are not always compatible with the substitution pattern of the substrates.…”