Either use CELL2STRUCT:
% Fake data:
Varnames = cellstr("X"+(1:18));
VarDec = randi(9,5,3,18);
% Convert to struct:
C = num2cell(VarDec,1:2);
S = cell2struct(C,Varnames,3)
Or a simple comma-separated list with STRUCT:
D = reshape(Varnames,1,[]);
D(2,:) = C;
S = struct(D{:})
