Alkenylstannanes, synthesis

The intramolecular coupling of organostannanes is applied to macrolide synthesis. In the zearalenone synthesis, no cyclization was observed between arylstannane and alkenyl iodide. However, intramolecular coupling take.s place between the alkenylstannane and aryl iodide in 706. A similar cyclization is possible by the reaction of the alkenylstannane 707 with enol triflate[579]. The coupling was applied to the preparation of the bicyclic 1,3-diene system 708[580]. 

A 1,2-metalate rearrangement of a higher order cuprate, known as a Kodenski rearrangement [64], was used as a key step in the synthesis of the marine antiinflammatory sesterterpenoid manoalide 95 (Scheme 9.20) [65]. Treatment of the alkenyl lithium 89 (prepared from the alkenylstannane 88 with s-BuLi in a diethyl ether-pentane mixture) with the homocuprate 91 (produced from iodoalkane 90) gave the iodoalkene 94 in 72% overall yield from 88. The reaction proceeds as fol-... 

One of the first cross-coupling reactions performed on solid supports was the Stille reaction [250] which is a paUadium-catalyzed reaction of a trialkylaryl or trialkylalkenyl stannane with an aromatic iodide, bromide or triflate. In contrast to the process in liquid-phase, the organotin reagent is easily removed from the solid-phase because of the subsequent washing processes. Immobilized aryl halides have been frequently coupled with aryl and alkenylstannanes, whereas stan-nanes attached to the solid support have been used less frequently for the StiUe reaction. An example is the synthesis of a benzodiazepine library by EUman et al. Recently, a Stille cross-couphng reaction has been employed in the synthesis of al-kenyldiarylmethanes (ADAM) series of non-nucleoside HlV-1 Reverse Transcriptase Inhibitors (Scheme 3.14) [251]. 

Coupling of aryl halides with alkenyl stannanes promoted through palladium metal catalysis, otherwise known as the Stille coupling, has many applications,22 including solid-phase variants (see Chapter 2).3-5 One of these is featured in Nicolaou and co-workers solid-phase synthesis of (5)-zearalenone wherein a resin-bound alkenylstannane undergoes a Stille cycli-... 

Hodgson, D. M. Chromium(ll)-mediated synthesis of (E)-alkenylstannanes from aldehydes and Bu3SnCHBr2. Tetrahedron Lett. 1992, 33, 5603-5604. 

Oxidative couplings. The synthesis of biaryls from aiylboronic acids and 1,3-dienes from alkenylstannanes- under mild conditions involves the Pd(0Ac)2-02 system. 

Alkenylstannanes. Hydrostannylation of 1-bromoalkynes by employing BUjSnH, (dba)jPd2, and PhjP provides ( )-alkenylstannanes. It is convenient to effect a Stille coupling immediately because the proper Pd catalyst is already present. From 1 -alkynes and 1-bromoalkenes the synthesis of 1,3-dienes requires only catalytic amounts of the tin reagent. 

Dibromomethyltributyltin reacts with aldehydes in the presence of CrCl2 and Lil via Bu3SnCHI2 and perhaps Bu3SnCH(Crm)2, to give is-alkenylstannanes (e.g equation 6-6)/ 21 22 Reactions of this type have been used in constructing the 1,3-diene units in the total synthesis of (-)-Macrolactin A and related compounds.23. 

The stereospecific Stille coupling of alkenyl bromides or iodides with alkenylstannanes is one of the most widely applied methods for the synthesis of dienes. Thus, a slight modification of the original method was applied in the coupling of alkenyl iodide 1 with (Z)-alkenylstannane 2, stereospecifically building a polyene as the last step in the synthesis of (—)-stipiamide (Scheme 5.4.1).25... 

Panek reported the syntheses of the anti-fnngal agents cystothiazoles A (100a) and B (101) from non-symmetrical bisthiazoles 98a,b, which were prepared by the regioselective coupling of bistriflate 96 with stannanes 97a,b (Scheme 5.4.19).This synthesis also made nse of a second Stille coupling of 98a,b with alkenylstannane 99. 

The coupling of benzyl halides with stannanes has been occasionally used in synthesis.One illustrative example is the total syntheses of piericidin A1 (119) and B1 (120).i2o in these syntheses a heterobenzylic Stille cross-coupling reaction of 116 with alkenylstannane 117 proceeded in the presence of a Pd(0) complex bearing bulky PrBuj as the ligand to give key intermediate 118 (Scheme 5.4.23). 

Despite the lack of examples of Friedel-Crafts acylations catalyzed by Lewis acids, - reactions of stannanes with acyl halides catalyzed by palladium species have found considerable use for the preparation of ketones. Since alkyl groups are only transferred slowly from tin, more rapid transfer to the acyl chloride is observed for alkynyl, alkenyl and allyl, as well as aryl and benzyl, groups. This leads to a versatile synthesis of ketones.Acylations of alkenylstannanes are both regio- and stereo-specific. 

Aromatic, aliphatic and heterocyclic acid chlorides all give high yields of ketones, [1,4] addition not being observed with a,3-unsaturated acid chlorides. This leads to a potentially very useful synthesis of divinyl ketones since, in contrast to Lewis acid catalyzed acylations of alkenes, under the neutral reaction conditions for the acylation of alkenylstannanes, cyclizations to cyclopentenones do not occur. 

Acylations. 2-Alkynoic esters arc the presence of (PhaP>4Pd and ba.se i DM Stille coupling. The usefulness preparation of arylcoumarin inhibitors < readily obtained from RSnBu, and brom The Stille coupling is accelerated b congested substrates has been developed coupling of alkenylstannanes using shgl synthesis of (—)-wodeshiol.- ... 

E)-l-Alkenylstannanes. A stereoselective synthesis starts from the hydrozirconation of 1-alkynes. Metal-metal exchange with retention of configuration is... 

In the total synthesis of strychnine, Overman prepared the alkenyl aryl ketone 67 in 80 % yield by the carbonylation of the aryl iodide 65 with the alkenylstannane 66 using AsPhs as a ligand [31]. 

In the total synthesis of amphidinolide A (57), a key step is the coupling of di(alkenylstannane) 54 with 55, which has the alkenyl iodide and allyl acetate moieties as reactive groups. The coupling proceeded in two steps when AsPh3 is used as a ligand. At first, reaction took place chemoselectively with the alkenyl iodide to give 56. Then cyclization of 56 occurred by the coupling of the allylic acetate moiety with the alkenylstannane in cyclohexane in the presence of LiCl to afford 57 [30]. 

Carbostannylation of alkynes generates cis-substituted alkenylstannanes and is one of the most useful reactions for stereoselective olefin synthesis. Treatment of tributyl-(phenylethynyl)tin 37 with a 1 2 mixture of [PdCl(7r-C3H5)]2-A -(2-diphenylphosphino benzylidene)-2-phenylethylamine (38) under an acetylene atmosphere in THF at... 

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