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5.2.17.9 Acylstannanes (Including S, Se, and Te Analogues) (Update 2014)

P. B. Wyatt

5.2.17.9.1 Applications of Acylstannanes in Organic Synthesis 5.2.17.9.1.1 Method 1: Synthesis of beta,Gamma-Unsaturated Ketones by Acylation of Allylic Esters with Acylstannanes

Acylstannanes 1 react with allyli esters 2 in the presence of palladium(II) trifluoroacetate as catalyst to provide good yields of beta,Gamma-unsaturated ketones 3 (_ Scheme 1).[1] Similar transformations may be achieved using acylsilanes in place of acylstannanes;[2] however, for introduction of the benzoyl group, the tin reagents provide much higher yields than their silicon counterparts, as well as a greatly reduced risk of isomerization to form the _,beta-un-saturated isomers of the ketone products.

Scheme 1 Synthesis of beta,Gamma-Unsaturated Ketones[1]

R1 R2 R3 Temp(°C) Yield(%) Ref Ph Me H rt 76 [1] (CH2)5Me Me H 50 71 [1] Ph Bu H rt 64 [1] Ph Me Ph rt 50 [1] (E)-1,4-Diphenylbut-3-en-1-one (3, R1 = R3 = Ph); Typical Procedure:[1]

A mixture of acylstannane 1 (R1 = Ph; R2 = Me; 121 mg, 0.50 mmol; as reported), allylic trifluoroacetate 2 (R3 = Ph; 115 mg, 0.50 mmol), Pd(OCOCF3)2 (8.0 mg, 0.025 mmol), and THF (0.25 mL) was stirred under argon at rt for 8 h. The product 3 was isolated following column chromatography (silica gel, hexane/EtOAc 9:1); yield: 50%.

5.2.17.9.1.2 Method 2: Synthesis of _-Oxoamides by Reaction of Stannanecarboxamides with Acyl Chlorides

The stannanecarboxamide 4 readily couples with acyl chlorides 5 to form _-oxoamides 6 (_ Scheme 2); no catalyst is needed.[3] Use of dichlorides, such as oxalyl chloride, allows polycarbonyl compounds to be prepared.

Scheme 2 Synthesis of _-Oxoamides by Reaction of Stannanecarboxamides with Acyl Chlorides[3]

R1 Temp(°C) Time(h) Yield(%) Ref Me rt 1 83 [3] iPr rt 1 87 [3] (E)-CH=CHPh rt 1 85 [3] Ph rt 3 85 [3] (CF2)2CF3 60 1 76 [3] N,N-Diisopropyl-2-oxopropanamide (6, R1 = Me); Typical Procedure:[3]

At rt, to a soln of iPr2NCOSnMe3 (4; 1.1 mmol) and docosane (0.37 mmol, internal standard for GC analysis) in benzene (2 mL) (CAUTION: carcinogen) was added AcCl (1.0 mmol) over 10 min and the soln was stirred at rt for 1 h. Volatiles were evaporated and the residue was subjected to column chromatography (silica gel, hexane then CH2Cl2) to give 2-oxoamide 6 (R1 = Me) as a colorless oil; yield: 83%.

5.2.17.9.1.3 Method 3: Synthesis of 3-(Trialkylstannyl)alk-2-enamides by Carbamoylstannylation of Terminal Alkynes

Terminal alkynes 7 undergo carbamoylstannylation upon treatment with the

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