Format of unnumbered chapter in TOC to be equal to the format of numbered chapter

In order to get the alignment as well as the correct font, one way is to write nothing to the toc and use addcontentsline with an empty chapter number as first argument of numberline{}{...} The command spacedlowsmallcaps from the arsclassica package is used to write the 'chapter' title within the TOC line.

I have added a wrapper, which automatically does this for your setup, assuming, that the chapter title is also intended as entry to the toc.

Please not the difference between addchap and addchapextended, I just did addchap{Sommario} effectively twice.

Extended version

documentclass[10pt,%                    
               a4paper,%                  
               twoside,openright,%        
%              oneside,openany,%         
               titlepage,%               
               headinclude,,footinclude,%  
               BCOR5mm,%                  
               cleardoublepage=empty,%    
               captions=tableheading,%       
               ]{scrreprt}    
usepackage[T1]{fontenc}

usepackage{lipsum}
usepackage[utf8]{inputenc}
usepackage[english,italian]{babel}       

usepackage[eulerchapternumbers,%        
            beramono,%                   
            eulermath,%                    
            pdfspacing,%                 
            listings,%                  
%           parts,%                       
            ]{classicthesis}   
usepackage{arsclassica}    


%newcommand{addchapextended}[1]{%  Old version without alignment
%addchap[noexpandspacedlowsmallcaps{#1}]{#1}%
%}%




makeatletter
newcommand{addchapextended}[1]{%
phantomsection%


makeatletter
newcommand{addchapextended}[1]{%
phantomsection%
addchap[]{#1}%  Do the unnumbered chapter head in the content section 
markboth{spacedlowsmallcaps{#1}}{spacedlowsmallcaps{#1}} 
pdfbookmark[0]{#1}{thepage::thechapter}%
%Add a contentsline to the TOC, omit the chapter number and align correctly
begingroup%
renewcommand{Hy@writebookmark}[5]{}{}{}{}{}%   Drop the automatic writing of bookmarks by addcontentsline%
addcontentsline{toc}{chapter}{%
numberline{}{noexpandspacedlowsmallcaps{#1}}}%
endgroup%
}%
makeatother%



begin{document}
hypersetup{pageanchor=false}
pagestyle{scrheadings} 
pagenumbering{gobble}


cleardoublepage
pdfbookmark{contentsname}{tableofcontents}
setcounter{tocdepth}{2}
tableofcontents
markboth{spacedlowsmallcaps{contentsname}}{spacedlowsmallcaps{contentsname}} 
cleardoublepage

hypersetup{pageanchor=true}
pagenumbering{arabic}

deftripstyle{pgnumtopouter}{}{}{pagemark}{}{}{}
renewcommand{chapterpagestyle}{pgnumtopouter}

cleardoublepage
phantomsection
%pdfbookmark{Sommario}{Sommario}
begingroup
letclearpagerelax
letcleardoublepagerelax
letcleardoublepagerelax

%phantomsection
%chapter*{Sommario}%
%addcontentsline{toc}{chapter}{protect{scshape Sommario}}

addchapextended{Sommario}%
addchap{Sommario}


%addchap[noexpandMakeTextLowercase{sffamilytextsc{Sommario}}]{Sommario}%

%addchap[sffamilytextsc{Lorem}]{Sommario}%

Qui Abstract in italiano

lipsum
lipsum
lipsum
lipsum
lipsum
vfill

selectlanguage{english}
pdfbookmark{Abstract}{Abstract}

addchapextended{Abstract}
addchapextended{Lorem}

lipsum
lipsum
lipsum
Qui abstract in inglese

selectlanguage{italian}

endgroup           

vfill

chapter{Lorem}
label{cap:lorem}
lipsum
lipsum
lipsum
lipsum

chapter{Lorem Nr. 2}

end{document}