Propargyl sulfonamides

Pyrroles can be synthesized from 3-pyrrolines 39 which can be prepared from a Crabbe reaction of propargyl sulfonamides 38 and selective cycloisomerization of the resulting allene intermediate. Subsequent oxidation of 3-pyrrohnes with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) lead to 2-alkyl and aryl pyrroles 40 in this domino process (14EJO2305). 

Reaction Procedure (Scheme 2.190) A mixture of 2-allgmylbromobenzene (0.2 mmol), propargylic sulfonamide (0.3 mmol), Pd(PhCN)2Cl2 (10 mol%), DPEPhos (10 mol%) and K2CO3 (0.4 mmol) in toluene (0.5 mL) was stirred at 80 °C. After completion of the reaction as indicated by TLC (usually 10 hours), the residue was purified immediately by flash chromatography on silica gel to provide indeno[l,2-c]pyrrole. 

When optically active allylic alcohol 6a and propargylic alcohol 6p were reacted with amides 2c and 2f, only racemic products 7ac, 7af, and 7pf were obtained (Scheme 2). The results suggested a mechanism through the formation of a carbe-nium intermediate. The observed racemization can also be ascribed to the reversibility of the present reaction. The result shown in Scheme 3 indicated that the reaction is reversible under the reaction conditions. When 7af was treated with 5 mol% of Bi(OTf)3 and KPF6 and 1 equiv of carbamate 2c, a mixture of 7af (28%) and 7ac (68%) was recovered after 1 h. The result suggested that Bi(OTf)3/KPF6 cleaved the C-N bond in 7af derived from sulfonamide 2f, and that 7ac is thermodynamically more stable than 7af. We assume that the desiccant (Drierite) had a beneficial effect on the reactions of substrates shown in Tables 10-12 because of the observed reversibility of the present reaction. In this reaction, the possibility... 

Complexation of propargyl aldehydes to cobalt also enhances the reactivity and enantioselectivity of the addition of alkylzinc reagents. This fact was used to create non-racemic enyne-ol 88 reacting the aldehyde 86 with bis-homoallylzinc in the presence of a chiral frzs-(sulfonamide) and Ti(OlPr)4. The resulting complexed substrate 87 underwent the PKR promoted by TMANO in a one pot fashion (Scheme 25) [122]. 

Carbonyl Allylation and Propargylation. Boron complex (8), derived from the bis(tosylamide) compound (3), transmeta-lates allylstannanes to form allylboranes (eq 12). The allylboranes can be combined without isolation with aldehydes at —78°C to afford homoallylic alcohols with high enantioselectivity (eq 13). On the basis of a single reported example, reagent control might be expected to overcome substrate control in additions to aldehydes containing an adjacent asymmetric center. The sulfonamide can be recovered by precipitation with diethyl ether during aqueous workup. Ease of preparation and recovery of the chiral controller makes this method one of the more useful available for allylation reactions. 

In the same vein but more in the style of Vollhardt s co-trimerisation is a remarkable series of reactions that combine three alkynes. One is propargyl alcohol and the other two are tethered by a sulfonamide.36 In the simple case 245, trimerisation with the Grubbs catalyst (see above) gives one positional isomer 244 of a benzo-pyrroline while Wilkinson s catalyst [(Ph3P)3RhCl] gives the other possible isomer 246. 

A-Alkylation of sulfonamides occurs at room temperature with benzylic, allylic and propargylic alcohols in the presence of Bi(OTf)3 and KPFg." ... 

Heck reactions involving nonaromatic components are particularly versatile synthetic processes. For example, 1,2,4-trienes and l,2-dien-4-ynes are readily prepared from propargyl carbonates." Intramolecular Heck cyclization followed by Diels-Alder or nucleophilic attackleads to bicyclic products. Substituted pyrrolidines and piperidines are formed by coupling of alkenyl sulfonamides with vinylic halides. ... 

There were a number of examples of the use of transition metal catalysts in cyclization reactions to form azepine derivatives. A paUadium(II) catalyst was employed for the intramolecular cyclization of sulfonamide-tethered propargylic carbonates (14AGE1915) and for the cyclization of N-tosyl... 

Hashmi et al. have developed a short and high-yielding synthetic approach towards functionalized indoline derivatives 227 following a reaction sequence that consists of a three-component aza-MBH reaction from furfural catalyzed by La(OTf)3 in combination with 3-HDQ, a simple sulfonamide propargylation and a gold-catalyzed cycloisomerization (Scheme 1.86). ... 

Ethers, esters, sulfonamides, and several other functional groups are well tolerated in this reaction. Notably, substrates bearing tertiary propargylic C-H bond could work as well. For example, ethynylcyclohexane gives trisubstituted alkenyl nitrile in 61 % yield. The ElZ ratio of the product, however, could not reach a satisfying level, given that great efforts have been made to improve it. 

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