Historically, single-metal organometallic species such as organolithium compounds have been the reagents of choice in synthetic organic chemistry for performing deprotonation reactions. Over the past few years, a complementary new class of metalating agents has started to emerge. Owing to a variable central metal (magnesium, zinc, or aluminum), variable ligands (both in their nature and number), and a variable second metallic center (an alkali metal such as lithium or sodium), "ate" complexes are highly versatile bases that exhibit a synergic chemistry which cannot be replicated by the homometallic magnesium, zinc, or aluminum compounds on their own. Deprotonation accomplished by using these organometallic ate complexes has opened up new perspectives in organic chemistry with unprecedented reactivities and sometimes unusual and unpredictable regioselectivities.

Deprotonative metalation using ate compounds: synergy, synthesis, and structure building

Stereocontrol in the synthesis of acyclic systems: applications to natural product synthesis

Organopalladium intermediates in organic synthesis

New general synthetic methods involving π-allylpalladium complexes as intermediates and neutral reaction conditions

Publisher Summary The chapter discusses the motions in proteins. Gelation of gelatin or precipitation of casein with mild acid are examples of reversible changes in which structural motility of the protein chains or subunits is recognized as playing a part. The sometimes reversible spreading of monolayers derived from mondisperse proteins provides some of the first evidence for the true plasticity of protein molecules and paved the way for the elegant demonstration of reversible conformational transitions. The tracing of the passage of an unfolded polypeptide chain to the compact, native structure is a primary concern of protein chemistry. One segment of polypeptide chain adapts its backbone and sidechain conformation to the structure of another segment in the process of forming the compact, functional structure of a protein was made particularly vivid by experiments on the reassociation of cleaved fragments. Overall translational and rotational motion is observed with a protein in solution, apart from any intramolecular motions. These overall motions are those that remain if the protein molecule is treated as a rigid matrix. Rotational reorientation of intramolecular components involves rotations about individual interatomic bonds. Concerted motions in proteins involve the movement of groups of side chains or segments of backbone relative to other structures. Motions of interacting ions and small molecules produce fluctuations in protein structure in addition to Brownian transfer of momentum. Time scales of various types of motions are important both for experimental recognition of the time-dependent processes and for analyzing their importance in the functional molecular mechanics. The chapter also discusses the dominant methods of observation that provide information about frequencies and amplitudes of motions in proteins.

Motions in proteins.

A new approach has been demonstrated for the regiospecific aldol synthesis by the simultaneous addition of α-halo carbonyl derivatives and aldehydes or ketones to a suspension of diethylaluminum chloride and zinc in tetrahydrofuran at low temperature. This technique is also employable under mild conditions for the Reformatsky reaction to give β-hiydroxy esters in excellent yield. One of the unique synthetic applications of this process is illustrated by the intramolecular cyclization of α-bromo esters of ω-hydroxy aldehyde, which produces macrolides, an important class of compounds in the antibiotic field.

Yoshizo Kitagawa

Papers

A new and highly effective aldol synthesis.

A new and highly effective aldol synthesis

Total synthesis of humulene. A stereoselective approach

Seven-membered rings via silyl enol ether participation in the olefin cyclization. Anti-Markownikoff cyclization in biomimetic terpene synthesis

Novel nonenzymic heterolysis of an allyl phosphate ester by organoaluminum reagents