Substrate-Controlled Domino Reactions of Crotonate-Derived Sulfur Ylides: Synthesis of Benzothiophene Derivatives

Abstract

Substrate-controlled domino reactions between thioaurones or their analogues and crotonate-derived sulfur ylides were developed and produced a broad spectrum of benzothiophene-fused pyran derivatives, substituted chromene derivatives. In these reactions, crotonate-derived sulfur ylides acting as two-carbon synthons (α and β carbons or β and γ carbons) in annulation reactions are reported for the first time. These investigations nicely complement and expand previously studied reactions of crotonate-derived sulfur ylides. In addition, reaction mechanisms for these domino reactions are proposed, one of which is supported by DFT calculations.

Synthesis of Benzothiophene‐Fused Oxa[6.6.5]tricyclic Skeletons through a Cinchonidine‐ or NaOH‐Promoted Quadruple Domino Sequence

“…First, O-Michael addition of D produces E with two hydrogen atoms (in the 2-and 4-positions) on the same face of the ring, which is kinetically more stable. [13] In terms of intermediate G,t he hydrogen adjacent to the aldehyde and the hydrogen adjacent to the oxygen are on the same faceo ft he ring, which facilitates the subsequent Witting reaction. The mechanism of the formation of 5 was similar to that of 3.…”

Construction of Oxepino[3,2‐b]indoles via [4+3] Annulation of 2‐Ylideneoxindoles with Crotonate‐Derived Sulfur Ylides

“…To our delight, the desired [4+3] annulation product 3 a was obtained in 30% yield. To improve the yield and try to obtain other unprecedented annulation products, [4c,f,o] various organic and inorganic bases such as DABCO, K 2 CO 3 , K 3 PO 4 , NaOH, t− BuOK and Cs 2 CO 3 were also tested (Table 1, entry 1–7), and Cs 2 CO 3 was founded to be the optimal choice (Table 1, entry 7). Interestingly, except for [4+3] annulation product 3 a , no other annulation products were produced under the above‐tested reaction conditions.…”

Recent Advances on Annulation Reactions with Allyl and Propargyl Sulfonium Salts

“…Aside from Meng's reports of [4 + 3] annulation of cyclic enones 20 and allyl sulfonium salts (see Scheme 12), the same group re-investigated this reaction and further disclosed their new discoveries. 27 position were also investigated, and 3-benzothiophenesubstituted chromene products 43 were observed in these reactions. The authors proposed that such formal [4 + 2] annulation might proceed through a cyclopropanation / vinylcyclopropane rearrangement process.…”

“…Aside from Meng's reports of [4+3] annulations of cyclic enones 20 and allyl sulfonium salts (see Scheme 12), the same group re-investigated this reaction and further disclosed their new discoveries. 27 As shown in Scheme 18, the reaction started with a [4+2] cyclization to afford an ylide intermediate I-18A. When the aryl-substituted compound 20 was used in the presence of N,N-diisopropylethylamine (DIPEA), the product 40 was obtained through the key intermediate I-18B.…”