Allenyl carbinol

Burger2 has shown that alkynes undergo both Lewis acid-catalyzed and thermal carbonyl-yne reactions with 3,3,3-trifluoropyruvates to give allenes. Reaction of 1 (Equation (2)) occurs to give a 1 1 mixture of diastereomeric allenyl carbinols 2. Alternatively, reaction of hexyne 1 and methyl trifluoropyruvate with MgBr2-OEt2 at low temperature afforded 2 as an 8 1 mixture of diastereomers. The thermal reaction does not suffer from allylic alcohol byproducts arising from reaction of the substrate with the Lewis acid.3... 

In the case of Pd-catalyzed reactions of aryl halides with allenyl carbinols 24, enones 27 [23] were obtained (Scheme 8). 

Scheme 9. Reactions of allenyl carbinols 24 and related amines 28. Mts = 2,4,6-trimethylbenzenesulfonyl.

Cyclizations. Substituted furans are formed from HgClj-catalyzed cyclization of allenyl carbinols which are derived from 3-methoxy-l-phenylthio-l-propyne. ... 

A Cr(III) complex of the binaphthyl that is 2,2 -disubstituted by a 7-t-butyl-8-hydiDxy-quinol-2-yl group (56) is the source of chirality in the allenyl carbinols produced from reaction of propargylic bromides with aldehydes. ... 

Esters of allenyl carbinols give 2-acyloxy-l,3-dienes on treatment with AuNTf2, which is complexed to (2, 4, 6 -triisopropyl-2-biphenyl)dicyclohexylphosphine. ... 

Reductive coupling. Cross coupling of ally lie alcohols with alkynes leads to 1,4-dienes using (i-PrO)3TiCl and c-C5H9MgCl." Allenyl carbinols react without loss of the hydroxyl group. ... 

Addition and substitution. Addition of allylindium reagents to allenyl carbinols affords linear products. A net l,3-butadien-2-ylation at the (3-carbon of p-acetoxy-p-lactams results when they are treated with indium and l,4-dibromo-2-butyne. ... 

Alternatively, carbene-complexed copper hydride species is involved in the transformation of alkynyl epoxides to allenyl carbinols using Cul, t-BuONa, PMHS and a imidazo-lium salt. ... 

Two synthetically interesting processes are the Sn2 reaction of the esters of allenyl carbinols with organozinc reagents to generate conjugated dienes, and the benzologue version (1,5-transpositional displacement) involving aUyltributylstannane. ... 

Rearrangement of allenyl carbinols by the ortho ester variation with trimethyl orthoacetate yields ( , )-dienes 20 together with small amounts of (Z.Z)-dienes 21 with ds > 90 % via chair transition state A, as long as R1 is a methyl group or hydrogen. When silicon-substituted substrates 18c and d are rearranged, the amount of 21 increases. This increase in 21 can be explained by transition state B. However, boatlike transition state C seems to be more likely because of favorable attraction between the methoxy and silyl groups662. 

Alkylation of acetals. When applied to mixed acetals bearing an a-stannylalkyl branch, the catalyzed reaction with alkynylstannanes gives propargyl ethers, which are precursors of allenyl carbinols. ... 

Gagosz reported a mild and efficient protocol for the synthesis of 1,3-butadien-2-ol esters from allenyl carbinol esters. The methodology proceeded smoothly using 1 mol% of gold complex XXIV, at room temperature and some of the compounds were fully converted after only five minutes. The. E-isomer was preferably obtained in most cases (Scheme 16.45). 

Scheme 16.45 Isomerisation of allenyl carbinol esters to l,3-butadien-2-ol esters.

C-H activation is an important and rapidly developing area of dendralene synthesis. In very recent years, several C2-C3 bond forming approaches to dendralenes involving C-H activation have been reported. In 2013, Glorius and coworkers developed a Rh(III)-catalyzed, Heck-type alkenyl C-H activation and coupling reaction with allenyl carbinol carbonates 205 and acrylamides 206 (Scheme 1.33) [157]. This new reaction performs well for the synthesis of highly substituted [3]dendralenes. 

Recently, allenyl carbinol esters have also been efficiently rearranged into buta-1,3-dien-2-ol esters via metal catalyzed transformations. Gold (1) catalysis has proven efficient under smooth conditions (CH2CI2 at room temperature) when using the biphenylphosphme-based catalyst 173. The stereoselectivity of the process depends on the substrate and favors the formation of the E isomer (Scheme 73) [157]. More recently, the use of rhodium catalysts in similar transformations has been reported to lead to higher E selectivities, although in harsher reaction conditions (Toluene at 120 °C) (Scheme 73) [158]. 

Scheme 73 Metal catalyzed isomerization of allenyl carbinol esters into buta-l,3-dien-2-ol esters...

Allenyl carbinol esters 60 (Scheme 35) form l,3-butadien-2-ol esters 61 under mild conditions with low catalyst loadings and good -selectivity [195]... 

Scheme 35 Gold(l)-catalyzed reaction of allenyl carbinol esters...

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