Additions of Organocopper Reagents and Heteroatom Nucleophiles to 1-Phenylseleno-2-(p-toluenesulfonyl)ethyne. Preparation of Vinyl and Allenic Sulfones and Formation of Michael, Anti-Michael, and Rearrangement Products
摘要:
1-Phenylseleno-2-(p-toluenesulfonyl)ethyne (4) was produced nearly quantitatively from p-(toluenesulfonyl)ethyne and benzeneselenenyl chloride. It underwent stereo- and regioselective syn-additions of organocopper reagents RCu(CN)Li to the beta-position of the sulfone moiety to afford adducts 5. Further reaction of the products with reagents RCu(SePh)Li resulted in substitution of the phenylseleno group with retention of configuration. Control of E,Z-stereochemistry in the product beta,beta-disubstituted vinyl sulfones is therefore achieved by the order of addition of the reagents. Selenoxide syn-elimination of adducts 5 afforded the corresponding allenic sulfones. The additions of amines and alkoxides to 4 produced the corresponding anti-Michael regioisomers (where attack occurred a to the sulfone group) as the major or sole products. The additions were highly stereoselective, proceeding by anti-addition in the anti-Michael series and by syn-addition in the corresponding Michael regioisomers. The reactions of 4 with thiolates and selenolates were more complex, affording rearranged adducts and Michael adducts as the major and minor products, respectively. The formation of the rearranged products can be rationalized by a series of addition-elimination processes. Phenylselenoethyne (43) underwent conjugate additions of pyrrolidine, sodium methoxide, sodium ethanethiolate, and benzeneselenolate anion, affording the corresponding cis isomers via anti-addition. The experiments with heteroatom nucleophiles and acetylenes 4 and 43 show that the phenylseleno group has a surprisingly large activating effect upon conjugate additions.
Preparation of Propargylic Sulfinates and their [2,3]-Sigmatropic Rearrangement to Allenic Sulfones
作者:Rama Rao Tata、Carissa S. Hampton、Michael Harmata
DOI:10.1002/adsc.201600986
日期:2017.4.3
scope of the [2,3]‐sigmatropic rearrangement of propargylic sulfinates to allenic sulfones by silver catalysis was expanded. A series of new propargylic sulfinate esters was generated from a variety of aromatic and heteroaromatic sulfonyl chlorides and their rearrangement to allenic sulfones is reported. In addition, the synthesis of propargylic sulfinate esters containing electron‐withdrawing benzenesulfonyl
Asymmetric oxidation of some aryl vinyl selenides (3) with Sharpless (A-C), modified Sharpless (D) or David oxidants (E-G) resulted in the formation of chiral allenic sulfones 5 of up to 42% enantiomeric excess (ee) via double asymmetric induction, i.e., asymmetric oxidation to selenoxide followed by its asymmetric elimination. The nature of aryl group of the selenides 3 showed a remarkable effect upon the ee of the product: o-nitrophenyl group (a) gave the highest ee, followed by o,p-dinitrophenyl (b), o-(trifluoromethyl)phenyl (e), and o-methoxyphenyl (f) groups, while phenyl (e) and 2-pyridyl (d) groups were not effective at all. The effects of aryl groups were kinetically analyzed by comparing the rate constants of both steps (k1 for oxidation step and k2 for elimination step) which were determined by H-1-NMR analysis of the concentration of 3, the intermediate selenoxides 4, and 5. As a result, it was disclosed that the ratio of these rate constants (k1/k2) Was closely related to the ee of the product; the smaller the ratio is, the larger the ee becomes.