Alkynes multistep

Baxendale IR, Ley SV, Mansfield AC et al (2009) Multistep synthesis using modular flow reactors Bestmann-Ohira reagent for the formation of alkynes and triazoles. Angew Chem Int Edit 48(22) 4017 021... 

Compound 99 reacts with alkynes to generate thieno[2,3-f]thiopyranthiones and thieno[3,2-f]thiopyranthiones. The ratio of isomers is typically 1 1. The reaction proceeds via a cycloaddition reaction and an unprecedented molecular rearrangement (Equation 35) <20050L791>. Thieno[2,3-f]- and [3,2-f]thiopyrans can be prepared from thiophene-2-carbaldehyde in a multistep synthesis that leads to the thienothiopyrans in excellent yields <1999J(P1)2639>. 

Concerned with the need for an exhaustive multistep preparation of the required alkenylcopper or alkenylzinc intermediates, which are traditionally accessed from alkenyllithum precursors derived from alkynes, Lipshutz and Wood developed a... 

Problem-Solving Strategy Multistep Synthesis 416 Summary Reactions of Alkynes 418 EssentialTerms 421 Study Problems 422... 

Use retrosynthetic analysis to solve multistep synthesis problems with alkynes as reagents, intermediates, or products. 

Multistep synthesis problems are useful for exercising your knowledge of organic reactions, and in Chapter 8 we illustrated a systematic approach to synthesis. Now we apply this approach to a fairly difficult problem emphasizing alkyne chemistry. The compound to be synthesized is cA-2-methylhex-4-en-3-ol. (The 3-ol means there is an alcohol —OH group on C3.)... 

Propose effective single-step and multistep syntheses of alkynes by eliminations from alkyl halides and by the additions and substitutions of acetylide ions. 

Use alkynes as starting materials and intermediates in one-step and multistep syntheses. 

Q Propose single-step and multistep syntheses of ketones and aldehydes from alcohols, alkenes, alkynes, carboxylic acids, nitriles, acid chlorides, esters, and aromatic compounds. Problems 18-55, 56, 60, and 64... 

There are also cases where addition of thiyi radicals to unsaturated carbon-carbon bonds is the crucial step for thiophene ring formation. Flash vacuum pyrolysis (FVP) of the phosphorus ylide 90 affords initially the alkyne 91, which produces thiyi radical with loss of methyl radical. Cyclization of the resulting radical affords thienothiophene 92 as the final product with loss of one more methyl radical (Scheme 20) <1995SL53>. FVP of ylide 93 results in a multistep cascade reaction leading to 7-(2-benzothienyl)benzofuran 94 (Scheme 21) <2001SL228>. 

In an imaginative construction of the angular triquinane ( )-hirsutene (158), Oppolzer and Robyr reported the carbonylative closure of allylic carbonate 155 to yield bicyclooctanes 156 and 157 (Scheme 6-27) [57]. In this multistep transformation, a alJylpalladium intermediate arising from the allylic carbonate 155 undergoes intramolecular Heck insertion of the pendant alkyne. Carbonylation of the resulting vinylpalladium intermediate, another Heck cyclization, and a second carbonylation then provide a mixture of acids, which after esterification yield esters 156 and 157 in good yield. 

The new, thermally stable 1-phosphadiene (134) has been prepared as shown, using a deficiency of DBU with excess DBU a mixture of (134) and (135) is obtained. Phosphonio-phospha-alkenes (136) has been prepared by elimination of an amino group of (137) by treatment with Lewis acids. Iminophosphines (138) and the phospha-alkyne (139) gave diphosphirenes (140) which rearranged at higher temperatures to the azadiphosphetines (141). The same phospha-alkyne (139) and tetrazines (142) gave the 1,2,3-azadi-phospholes (143) a plausible multistep mechanism for this unusual reaction is proposed. 

Chapter 6 covers the reactions of alkynes—hydrocarbons that contain carbon-carbon triple bonds. Because alkenes and alkynes both have reactive carbon-carbon tt bonds, you will discover that their reactions have many similarities. This chapter will also introduce you to some of the techniques chemists use to design syntheses of organic compounds, and you will then have your first opportunity to design a multistep synthesis. 

CHAPTER 6 Reactions of Alkynes Introduction to Multistep Synthesis... 

Nickel(0)-catalyzed [2 + 2 + 2] cocyclization of the precursor (177) in the presence of several chiral ligands afforded the chiral tetrahydroisoquinoline (178) in a novel asymmetric cycloaddition. Compound (178) could be transformed into the benzo[a]quinolizidine (180), albeit in modest enantiomeric excess, through a multistep route involving extension of the alkynic side chain at C-1 to yield (179), introduction of a cu halogen atom, reduction of the triple bond, A(-deprotection and final eyelization (Scheme 29) <94J0C6133>. 

One of the early examples of a furan IMDA reaction involved a multistep route to a precursor alkyne that gave a mixture of two diastereomeric cycloadducts as an entry to a functionalized gibbane <82TL329i>. The protocol was extended to a relatively short route to gibberelins, for example ( )GA5, and made use of an alkyne-furan IMDA reaction. The IMDA reaction, when carried out in benzene at 80°C proceeded slowly and gave a low yield of a 3 1 mixture in which the required... 

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